autocomplete to suggestions

canvas/CANVAS_MIGRATION.md

@@ -2,7 +2,7 @@
 
 ## Overview
 
-This guide covers the migration from the legacy canvas library structure to the new clean, modular architecture. The new design separates core canvas functionality from autocomplete features, providing better type safety and maintainability.
+This guide covers the migration from the legacy canvas library structure to the new clean, modular architecture. The new design separates core canvas functionality from suggestions features, providing better type safety and maintainability.
 
 ## Key Changes
 
@@ -10,7 +10,7 @@ This guide covers the migration from the legacy canvas library structure to the
 ```
 # Old Structure (LEGACY)
 src/
-├── state.rs              # Mixed canvas + autocomplete
+├── state.rs              # Mixed canvas + suggestions
 ├── actions/edit.rs       # Mixed concerns
 ├── gui/render.rs         # Everything together
 └── suggestions.rs        # Legacy file
@@ -21,9 +21,9 @@ src/
 │   ├── state.rs         # CanvasState trait only
 │   ├── actions/edit.rs  # Canvas actions only
 │   └── gui.rs           # Canvas rendering
-├── autocomplete/         # Rich autocomplete features
+├── suggestions/         # Suggestions dropdown features (not inline autocomplete)
-│   ├── state.rs         # AutocompleteCanvasState trait
+│   ├── state.rs         # Suggestion provider types
-│   ├── types.rs         # SuggestionItem, AutocompleteState
+│   ├── gui.rs           # Suggestions dropdown rendering
 │   ├── actions.rs       # Autocomplete actions
 │   └── gui.rs           # Autocomplete dropdown rendering
 └── dispatcher.rs         # Action routing
@@ -31,7 +31,7 @@ src/
 
 ### 2. **Trait Separation**
 - **CanvasState**: Core form functionality (navigation, input, validation)
-- **AutocompleteCanvasState**: Optional rich autocomplete features
+- Suggestions module: Optional dropdown suggestions support
 
 ### 3. **Rich Suggestions**
 Replaced simple string suggestions with typed, rich suggestion objects.
@@ -93,34 +93,29 @@ impl CanvasState for YourFormState {
 
 ### Step 3: Implement Rich Autocomplete (Optional)
 
-**If you want rich autocomplete features:**
+**If you want suggestions dropdown features:**
 
 ```rust
-use canvas::autocomplete::{AutocompleteCanvasState, SuggestionItem, AutocompleteState};
+use canvas::{SuggestionItem};
 
-impl AutocompleteCanvasState for YourFormState {
+impl YourFormState {
-    type SuggestionData = YourDataType; // e.g., Hit, CustomRecord, etc.
+    fn supports_suggestions(&self, field_index: usize) -> bool {
-
+        // Define which fields support suggestions
-    fn supports_autocomplete(&self, field_index: usize) -> bool {
-        // Define which fields support autocomplete
         matches!(field_index, 2 | 3 | 5) // Example: only certain fields
     }
 
-    fn autocomplete_state(&self) -> Option<&AutocompleteState<Self::SuggestionData>> {
+    // Manage your own suggestion state or rely on FormEditor APIs
-        Some(&self.autocomplete)
-    }
 
-    fn autocomplete_state_mut(&mut self) -> Option<&mut AutocompleteState<Self::SuggestionData>> {
+    // Manage your own suggestion state or rely on FormEditor APIs
-        Some(&mut self.autocomplete)
-    }
 }
 ```
 
-**Add autocomplete field to your state:**
+**Add suggestions storage to your state (optional, if you need to persist outside the editor):**
 ```rust
 pub struct YourFormState {
     // ... existing fields
-    pub autocomplete: AutocompleteState<YourDataType>,
+    // Optional: your own suggestions cache if needed
+    // pub suggestion_cache: Vec<SuggestionItem>,
 }
 ```
 
@@ -149,9 +144,9 @@ form_state.set_autocomplete_suggestions(suggestions);
 
 **Old rendering:**
 ```rust
-// Manual autocomplete rendering
+// Manual suggestions rendering
-if form_state.autocomplete_active {
+if editor.is_suggestions_active() {
-    render_autocomplete_dropdown(/* ... */);
+    suggestions::gui::render_suggestions_dropdown(/* ... */);
 }
 ```
 
@@ -162,13 +157,12 @@ use canvas::canvas::render_canvas;
 
 let active_field_rect = render_canvas(f, area, form_state, theme, edit_mode, highlight_state);
 
-// Optional: Rich autocomplete (if implementing AutocompleteCanvasState)
+// Suggestions dropdown (if active)
-if form_state.is_autocomplete_active() {
+if editor.is_suggestions_active() {
-    if let Some(autocomplete_state) = form_state.autocomplete_state() {
+    canvas::suggestions::render_suggestions_dropdown(
-        canvas::autocomplete::render_autocomplete_dropdown(
+        f, f.area(), active_field_rect.unwrap(), theme, &editor
-            f, f.area(), active_field_rect.unwrap(), theme, autocomplete_state
+    );
-        );
+}
-    }
 }
 ```
 
@@ -181,16 +175,16 @@ form_state.deactivate_suggestions();
 
 # NEW - Option A: Add your own method
 impl YourFormState {
-    pub fn deactivate_autocomplete(&mut self) {
+    pub fn deactivate_suggestions(&mut self) {
         self.autocomplete_active = false;
         self.autocomplete_suggestions.clear();
         self.selected_suggestion_index = None;
     }
 }
-form_state.deactivate_autocomplete();
+editor.ui_state_mut().deactivate_suggestions();
 
-# NEW - Option B: Use rich autocomplete trait
+# NEW - Option B: Suggestions via editor APIs
-form_state.deactivate_autocomplete(); // If implementing AutocompleteCanvasState
+editor.ui_state_mut().deactivate_suggestions();
 ```
 
 ## Benefits of New Architecture
@@ -217,8 +211,8 @@ let suggestions: Vec<SuggestionItem<UserRecord>> = vec![
 - **Display Overrides**: Show friendly text while storing normalized data
 
 ### 4. **Future-Proof**
-- Easy to add new autocomplete features
+- Easy to add new suggestion features
-- Canvas features don't interfere with autocomplete
+- Canvas features don't interfere with suggestions
 - Modular: Use only what you need
 
 ## Advanced Features
@@ -262,7 +256,7 @@ SuggestionItem::new(user, "John Doe (Manager)".to_string(), "123".to_string());
 ## Breaking Changes Summary
 
 1. **Import paths changed**: Add `canvas::` or `dispatcher::` prefixes
-2. **Legacy suggestion methods removed**: Replace with rich autocomplete or custom methods
+2. **Legacy suggestion methods removed**: Replace with SuggestionItem-based dropdown or custom methods
 3. **No more simple suggestions**: Use `SuggestionItem` for typed suggestions
 4. **Trait split**: `AutocompleteCanvasState` is now separate and optional
 
@@ -283,11 +277,11 @@ SuggestionItem::new(user, "John Doe (Manager)".to_string(), "123".to_string());
 
 - [ ] Updated all import paths
 - [ ] Removed legacy methods from CanvasState implementation
-- [ ] Added custom autocomplete methods if needed
+- [ ] Added custom suggestion methods if needed
-- [ ] Updated suggestion usage to SuggestionItem
+- [ ] Updated usage to SuggestionItem
 - [ ] Updated rendering calls
 - [ ] Tested form functionality
-- [ ] Tested autocomplete functionality (if using)
+- [ ] Tested suggestions functionality (if using)
 
 ## Example: Complete Migration
 
@@ -305,29 +299,25 @@ impl CanvasState for FormState {
 **After:**
 ```rust
 use canvas::canvas::{CanvasState, CanvasAction};
-use canvas::autocomplete::{AutocompleteCanvasState, SuggestionItem};
+use canvas::SuggestionItem;
 
 impl CanvasState for FormState {
-    // Only core canvas methods, no suggestion methods
+    // Only core canvas methods
     fn current_field(&self) -> usize { /* ... */ }
     fn get_current_input(&self) -> &str { /* ... */ }
     // ... other core methods only
 }
 
-impl AutocompleteCanvasState for FormState {
+// Use FormEditor + SuggestionsProvider for suggestions dropdown
     type SuggestionData = Hit;
     
-    fn supports_autocomplete(&self, field_index: usize) -> bool {
+    fn supports_suggestions(&self, field_index: usize) -> bool {
         self.fields[field_index].is_link
     }
     
-    fn autocomplete_state(&self) -> Option<&AutocompleteState<Self::SuggestionData>> {
+    // Maintain suggestion state through FormEditor and DataProvider
-        Some(&self.autocomplete)
-    }
     
-    fn autocomplete_state_mut(&mut self) -> Option<&mut AutocompleteState<Self::SuggestionData>> {
+    // Maintain suggestion state through FormEditor and DataProvider
-        Some(&mut self.autocomplete)
-    }
 }
 ```
 

canvas/Cargo.toml

@@ -30,15 +30,15 @@ tokio-test = "0.4.4"
 
 [features]
 default = []
-gui = ["ratatui"]
+gui = ["ratatui", "crossterm"]
-autocomplete = ["tokio"]
+suggestions = ["tokio"]
 cursor-style = ["crossterm"]
 validation = ["regex"]
 
 [[example]]
-name = "autocomplete"
+name = "suggestions"
-required-features = ["autocomplete", "gui"]
+required-features = ["suggestions", "gui", "cursor-style"]
-path = "examples/autocomplete.rs"
+path = "examples/suggestions.rs"
 
 [[example]]
 name = "canvas_gui_demo"
@@ -48,3 +48,19 @@ path = "examples/canvas_gui_demo.rs"
 [[example]]
 name = "validation_1"
 required-features = ["gui", "validation"]
+
+[[example]]
+name = "validation_2"
+required-features = ["gui", "validation"]
+
+[[example]]
+name = "validation_3"
+required-features = ["gui", "validation"]
+
+[[example]]
+name = "validation_4"
+required-features = ["gui", "validation"]
+
+[[example]]
+name = "validation_5"
+required-features = ["gui", "validation"]

canvas/README.md

@@ -7,7 +7,7 @@ A reusable, type-safe canvas system for building form-based TUI applications wit
 - **Type-Safe Actions**: No more string-based action names - everything is compile-time checked
 - **Generic Design**: Implement `CanvasState` once, get navigation, editing, and suggestions for free
 - **Vim-Like Experience**: Modal editing with familiar keybindings
-- **Suggestion System**: Built-in autocomplete and suggestions support
+- **Suggestion System**: Built-in suggestions dropdown support
 - **Framework Agnostic**: Works with any TUI framework or raw terminal handling
 - **Async Ready**: Full async/await support for modern Rust applications
 - **Batch Operations**: Execute multiple actions atomically
@@ -144,7 +144,7 @@ pub enum CanvasAction {
 
 ## 🔧 Advanced Features
 
-### Suggestions and Autocomplete
+### Suggestions Dropdown (not inline autocomplete)
 
 ```rust
 impl CanvasState for MyForm {
@@ -170,7 +170,7 @@ impl CanvasState for MyForm {
             CanvasAction::SelectSuggestion => {
                 if let Some(suggestion) = self.suggestions.get_selected() {
                     *self.get_current_input_mut() = suggestion.clone();
-                    self.deactivate_autocomplete();
+                    self.deactivate_suggestions();
                     Some("Applied suggestion".to_string())
                 }
                 None

canvas/examples/canvas_cursor_auto.rs

@@ -346,7 +346,7 @@ impl DataProvider for CursorDemoData {
         self.fields[index].1 = value;
     }
 
-    fn supports_autocomplete(&self, _field_index: usize) -> bool {
+    fn supports_suggestions(&self, _field_index: usize) -> bool {
         false
     }
 

canvas/examples/full_canvas_demo.rs

@@ -345,7 +345,7 @@ impl DataProvider for FullDemoData {
         self.fields[index].1 = value;
     }
 
-    fn supports_autocomplete(&self, _field_index: usize) -> bool {
+    fn supports_suggestions(&self, _field_index: usize) -> bool {
         false
     }
 

canvas/examples/suggestions.rs

@@ -1,5 +1,5 @@
-// examples/autocomplete.rs
+// examples/suggestions.rs
-// Run with: cargo run --example autocomplete --features "autocomplete,gui"
+// Run with: cargo run --example suggestions --features "suggestions,gui"
 
 use std::io;
 use crossterm::{
@@ -22,8 +22,8 @@ use canvas::{
         modes::AppMode,
         theme::CanvasTheme,
     },
-    autocomplete::gui::render_autocomplete_dropdown,
+    suggestions::gui::render_suggestions_dropdown,
-    FormEditor, DataProvider, AutocompleteProvider, SuggestionItem,
+    FormEditor, DataProvider, SuggestionsProvider, SuggestionItem,
 };
 
 use async_trait::async_trait;
@@ -108,7 +108,7 @@ impl DataProvider for ContactForm {
         }
     }
     
-    fn supports_autocomplete(&self, field_index: usize) -> bool {
+    fn supports_suggestions(&self, field_index: usize) -> bool {
         field_index == 1 // Only email field
     }
 }
@@ -120,11 +120,9 @@ impl DataProvider for ContactForm {
 struct EmailAutocomplete;
 
 #[async_trait]
-impl AutocompleteProvider for EmailAutocomplete {
+impl SuggestionsProvider for EmailAutocomplete {
-    type SuggestionData = EmailSuggestion;
-    
     async fn fetch_suggestions(&mut self, _field_index: usize, query: &str) 
-        -> Result<Vec<SuggestionItem<Self::SuggestionData>>> 
+        -> Result<Vec<SuggestionItem>> 
     {
         // Extract domain part from email
         let (email_prefix, domain_part) = if let Some(at_pos) = query.find('@') {
@@ -153,10 +151,6 @@ impl AutocompleteProvider for EmailAutocomplete {
                 if domain.starts_with(&domain_part) || domain_part.is_empty() {
                     let full_email = format!("{}@{}", email_prefix, domain);
                     results.push(SuggestionItem {
-                        data: EmailSuggestion {
-                            email: full_email.clone(),
-                            provider: provider.to_string(),
-                        },
                         display_text: format!("{} ({})", full_email, provider),
                         value_to_store: full_email,
                     });
@@ -175,7 +169,7 @@ impl AutocompleteProvider for EmailAutocomplete {
 
 struct AppState {
     editor: FormEditor<ContactForm>,
-    autocomplete: EmailAutocomplete,
+    suggestions_provider: EmailAutocomplete,
     debug_message: String,
 }
 
@@ -190,8 +184,8 @@ impl AppState {
         
         Self {
             editor,
-            autocomplete: EmailAutocomplete,
+            suggestions_provider: EmailAutocomplete,
-            debug_message: "Type in email field, Tab to trigger autocomplete, Enter to select, Esc to cancel".to_string(),
+            debug_message: "Type in email field, Tab to trigger suggestions, Enter to select, Esc to cancel".to_string(),
         }
     }
 }
@@ -207,14 +201,14 @@ async fn handle_key_press(key: KeyCode, modifiers: KeyModifiers, state: &mut App
 
     // Handle input based on key
     let result = match key {
-        // === AUTOCOMPLETE KEYS ===
+        // === SUGGESTIONS KEYS ===
         KeyCode::Tab => {
-            if state.editor.is_autocomplete_active() {
+            if state.editor.is_suggestions_active() {
-                state.editor.autocomplete_next();
+                state.editor.suggestions_next();
                 Ok("Navigated to next suggestion".to_string())
-            } else if state.editor.data_provider().supports_autocomplete(state.editor.current_field()) {
+            } else if state.editor.data_provider().supports_suggestions(state.editor.current_field()) {
-                state.editor.trigger_autocomplete(&mut state.autocomplete).await
+                state.editor.trigger_suggestions(&mut state.suggestions_provider).await
-                    .map(|_| "Triggered autocomplete".to_string())
+                    .map(|_| "Triggered suggestions".to_string())
             } else {
                 state.editor.move_to_next_field();
                 Ok("Moved to next field".to_string())
@@ -222,8 +216,8 @@ async fn handle_key_press(key: KeyCode, modifiers: KeyModifiers, state: &mut App
         }
 
         KeyCode::Enter => {
-            if state.editor.is_autocomplete_active() {
+            if state.editor.is_suggestions_active() {
-                if let Some(applied) = state.editor.apply_autocomplete() {
+                if let Some(applied) = state.editor.apply_suggestion() {
                     Ok(format!("Applied: {}", applied))
                 } else {
                     Ok("No suggestion to apply".to_string())
@@ -235,9 +229,9 @@ async fn handle_key_press(key: KeyCode, modifiers: KeyModifiers, state: &mut App
         }
 
         KeyCode::Esc => {
-            if state.editor.is_autocomplete_active() {
+            if state.editor.is_suggestions_active() {
-                // Autocomplete will be cleared automatically by mode change
+                // Suggestions will be cleared automatically by mode change
-                Ok("Cancelled autocomplete".to_string())
+                Ok("Cancelled suggestions".to_string())
             } else {
                 // Toggle between edit and readonly mode
                 let new_mode = match state.editor.mode() {
@@ -324,9 +318,9 @@ fn ui(f: &mut Frame, state: &AppState, theme: &DemoTheme) {
         theme,
     );
 
-    // Render autocomplete dropdown if active
+    // Render suggestions dropdown if active
     if let Some(input_rect) = active_field_rect {
-        render_autocomplete_dropdown(
+        render_suggestions_dropdown(
             f,
             chunks[0],
             input_rect,
@@ -336,8 +330,8 @@ fn ui(f: &mut Frame, state: &AppState, theme: &DemoTheme) {
     }
 
     // Status info
-    let autocomplete_status = if state.editor.is_autocomplete_active() {
+    let autocomplete_status = if state.editor.is_suggestions_active() {
-        if state.editor.ui_state().is_autocomplete_loading() {
+        if state.editor.ui_state().is_suggestions_loading() {
             "Loading suggestions..."
         } else if !state.editor.suggestions().is_empty() {
             "Use Tab to navigate, Enter to select, Esc to cancel"
@@ -345,7 +339,7 @@ fn ui(f: &mut Frame, state: &AppState, theme: &DemoTheme) {
             "No suggestions found"
         }
     } else {
-        "Tab to trigger autocomplete"
+        "Tab to trigger suggestions"
     };
 
     let status_lines = vec![
@@ -354,9 +348,9 @@ fn ui(f: &mut Frame, state: &AppState, theme: &DemoTheme) {
             state.editor.current_field() + 1, 
             state.editor.data_provider().field_count(), 
             state.editor.cursor_position()))),
-        Line::from(Span::raw(format!("Autocomplete: {}", autocomplete_status))),
+        Line::from(Span::raw(format!("Suggestions: {}", autocomplete_status))),
         Line::from(Span::raw(state.debug_message.clone())),
-        Line::from(Span::raw("F10: Quit | Tab: Trigger/Navigate autocomplete | Enter: Select | Esc: Cancel/Toggle mode")),
+        Line::from(Span::raw("F10: Quit | Tab: Trigger/Navigate suggestions | Enter: Select | Esc: Cancel/Toggle mode")),
     ];
 
     let status = Paragraph::new(status_lines)

canvas/examples/validation_1.rs

@@ -447,7 +447,7 @@ impl DataProvider for ValidationDemoData {
         self.fields[index].1 = value;
     }
 
-    fn supports_autocomplete(&self, _field_index: usize) -> bool {
+    fn supports_suggestions(&self, _field_index: usize) -> bool {
         false
     }
 

canvas/examples/validation_4.rs

@@ -0,0 +1,738 @@
+/* examples/validation_4.rs
+   Enhanced Feature 4 Demo: Multiple custom formatters with comprehensive edge cases
+   
+   Demonstrates:
+   - Multiple formatter types: PSC, Phone, Credit Card, Date
+   - Edge case handling: incomplete input, invalid chars, overflow
+   - Real-time validation feedback and format preview
+   - Advanced cursor position mapping
+   - Raw vs formatted data separation
+   - Error handling and fallback behavior
+
+*/
+
+#![allow(clippy::needless_return)]
+
+#[cfg(not(all(feature = "validation", feature = "gui")))]
+compile_error!(
+    "This example requires the 'validation' and 'gui' features. \
+     Run with: cargo run --example validation_4 --features \"gui,validation\""
+);
+
+use std::io;
+use std::sync::Arc;
+
+use crossterm::{
+    event::{
+        self, DisableMouseCapture, EnableMouseCapture, Event, KeyCode, KeyModifiers,
+    },
+    execute,
+    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
+};
+use ratatui::{
+    backend::{Backend, CrosstermBackend},
+    layout::{Constraint, Direction, Layout, Rect},
+    style::{Color, Style},
+    text::{Line, Span},
+    widgets::{Block, Borders, Paragraph, Wrap},
+    Frame, Terminal,
+};
+
+use canvas::{
+    canvas::{gui::render_canvas_default, modes::AppMode},
+    DataProvider, FormEditor,
+    ValidationConfig, ValidationConfigBuilder,
+    CustomFormatter, FormattingResult,
+};
+
+/// PSC (Postal Code) Formatter: "01001" -> "010 01"
+struct PSCFormatter;
+
+impl CustomFormatter for PSCFormatter {
+    fn format(&self, raw: &str) -> FormattingResult {
+        if raw.is_empty() {
+            return FormattingResult::success("");
+        }
+        
+        // Validate: only digits allowed
+        if !raw.chars().all(|c| c.is_ascii_digit()) {
+            return FormattingResult::error("PSC must contain only digits");
+        }
+        
+        let len = raw.chars().count();
+        match len {
+            0 => FormattingResult::success(""),
+            1..=3 => FormattingResult::success(raw),
+            4 => FormattingResult::warning(
+                format!("{} ", &raw[..3]), 
+                "PSC incomplete (4/5 digits)"
+            ),
+            5 => {
+                let formatted = format!("{} {}", &raw[..3], &raw[3..]);
+                if raw == "00000" {
+                    FormattingResult::warning(formatted, "Invalid PSC: 00000")
+                } else {
+                    FormattingResult::success(formatted)
+                }
+            },
+            _ => FormattingResult::error("PSC too long (max 5 digits)"),
+        }
+    }
+}
+
+/// Phone Number Formatter: "1234567890" -> "(123) 456-7890"
+struct PhoneFormatter;
+
+impl CustomFormatter for PhoneFormatter {
+    fn format(&self, raw: &str) -> FormattingResult {
+        if raw.is_empty() {
+            return FormattingResult::success("");
+        }
+        
+        // Only digits allowed
+        if !raw.chars().all(|c| c.is_ascii_digit()) {
+            return FormattingResult::error("Phone must contain only digits");
+        }
+        
+        let len = raw.chars().count();
+        match len {
+            0 => FormattingResult::success(""),
+            1..=3 => FormattingResult::success(format!("({})", raw)),
+            4..=6 => FormattingResult::success(format!("({}) {}", &raw[..3], &raw[3..])),
+            7..=10 => FormattingResult::success(format!("({}) {}-{}", &raw[..3], &raw[3..6], &raw[6..])),
+            10 => {
+                let formatted = format!("({}) {}-{}", &raw[..3], &raw[3..6], &raw[6..]);
+                FormattingResult::success(formatted)
+            },
+            _ => FormattingResult::warning(
+                format!("({}) {}-{}", &raw[..3], &raw[3..6], &raw[6..10]),
+                "Phone too long (extra digits ignored)"
+            ),
+        }
+    }
+}
+
+/// Credit Card Formatter: "1234567890123456" -> "1234 5678 9012 3456"
+struct CreditCardFormatter;
+
+impl CustomFormatter for CreditCardFormatter {
+    fn format(&self, raw: &str) -> FormattingResult {
+        if raw.is_empty() {
+            return FormattingResult::success("");
+        }
+        
+        if !raw.chars().all(|c| c.is_ascii_digit()) {
+            return FormattingResult::error("Card number must contain only digits");
+        }
+        
+        let mut formatted = String::new();
+        for (i, ch) in raw.chars().enumerate() {
+            if i > 0 && i % 4 == 0 {
+                formatted.push(' ');
+            }
+            formatted.push(ch);
+        }
+        
+        let len = raw.chars().count();
+        match len {
+            0..=15 => FormattingResult::warning(formatted, format!("Card incomplete ({}/16 digits)", len)),
+            16 => FormattingResult::success(formatted),
+            _ => FormattingResult::warning(formatted, "Card too long (extra digits shown)"),
+        }
+    }
+}
+
+
+
+
+
+
+/// Date Formatter: "12012024" -> "12/01/2024"
+struct DateFormatter;
+
+impl CustomFormatter for DateFormatter {
+    fn format(&self, raw: &str) -> FormattingResult {
+        if raw.is_empty() {
+            return FormattingResult::success("");
+        }
+        
+        if !raw.chars().all(|c| c.is_ascii_digit()) {
+            return FormattingResult::error("Date must contain only digits");
+        }
+        
+        let len = raw.len();
+        match len {
+            0 => FormattingResult::success(""),
+            1..=2 => FormattingResult::success(raw.to_string()),
+            3..=4 => FormattingResult::success(format!("{}/{}", &raw[..2], &raw[2..])),
+            5..=8 => FormattingResult::success(format!("{}/{}/{}", &raw[..2], &raw[2..4], &raw[4..])),
+            8 => {
+                let month = &raw[..2];
+                let day = &raw[2..4];
+                let year = &raw[4..];
+                
+                // Basic validation
+                let m: u32 = month.parse().unwrap_or(0);
+                let d: u32 = day.parse().unwrap_or(0);
+                
+                if m == 0 || m > 12 {
+                    FormattingResult::warning(
+                        format!("{}/{}/{}", month, day, year),
+                        "Invalid month (01-12)"
+                    )
+                } else if d == 0 || d > 31 {
+                    FormattingResult::warning(
+                        format!("{}/{}/{}", month, day, year),
+                        "Invalid day (01-31)"
+                    )
+                } else {
+                    FormattingResult::success(format!("{}/{}/{}", month, day, year))
+                }
+            },
+            _ => FormattingResult::error("Date too long (MMDDYYYY format)"),
+        }
+    }
+}
+
+// Enhanced demo data with multiple formatter types
+struct MultiFormatterDemoData {
+    fields: Vec<(String, String)>,
+}
+
+impl MultiFormatterDemoData {
+    fn new() -> Self {
+        Self {
+            fields: vec![
+                ("🏁 PSC (01001)".to_string(), "".to_string()),
+                ("📞 Phone (1234567890)".to_string(), "".to_string()),
+                ("💳 Credit Card (16 digits)".to_string(), "".to_string()),
+                ("📅 Date (12012024)".to_string(), "".to_string()),
+                ("📝 Plain Text".to_string(), "".to_string()),
+            ],
+        }
+    }
+}
+
+impl DataProvider for MultiFormatterDemoData {
+    fn field_count(&self) -> usize {
+        self.fields.len()
+    }
+    
+    fn field_name(&self, index: usize) -> &str {
+        &self.fields[index].0
+    }
+    
+    fn field_value(&self, index: usize) -> &str {
+        &self.fields[index].1
+    }
+    
+    fn set_field_value(&mut self, index: usize, value: String) {
+        self.fields[index].1 = value;
+    }
+
+    #[cfg(feature = "validation")]
+    fn validation_config(&self, field_index: usize) -> Option<ValidationConfig> {
+        match field_index {
+            0 => Some(ValidationConfigBuilder::new()
+                .with_custom_formatter(Arc::new(PSCFormatter))
+                .with_max_length(5)
+                .build()),
+            1 => Some(ValidationConfigBuilder::new()
+                .with_custom_formatter(Arc::new(PhoneFormatter))
+                .with_max_length(12)
+                .build()),
+            2 => Some(ValidationConfigBuilder::new()
+                .with_custom_formatter(Arc::new(CreditCardFormatter))
+                .with_max_length(20)
+                .build()),
+            3 => Some(ValidationConfigBuilder::new()
+                .with_custom_formatter(Arc::new(DateFormatter))
+                .with_max_length(8)
+                .build()),
+            4 => Some(ValidationConfigBuilder::new()
+                .with_custom_formatter(Arc::new(DateFormatter))
+                .with_max_length(8)
+                .build()),
+            _ => None, // Plain text field - no formatter
+        }
+    }
+}
+
+// Enhanced demo editor with comprehensive status tracking
+struct EnhancedDemoEditor<D: DataProvider> {
+    editor: FormEditor<D>,
+    debug_message: String,
+    validation_enabled: bool,
+    show_raw_data: bool,
+    show_cursor_details: bool,
+    example_mode: usize,
+}
+
+impl<D: DataProvider> EnhancedDemoEditor<D> {
+    fn new(data_provider: D) -> Self {
+        let mut editor = FormEditor::new(data_provider);
+        editor.set_validation_enabled(true);
+
+        Self {
+            editor,
+            debug_message: "🧩 Enhanced Custom Formatter Demo - Multiple formatters with rich edge cases!".to_string(),
+            validation_enabled: true,
+            show_raw_data: false,
+            show_cursor_details: false,
+            example_mode: 0,
+        }
+    }
+
+    // Field type detection
+    fn current_field_type(&self) -> &'static str {
+        match self.editor.current_field() {
+            0 => "PSC",
+            1 => "Phone",
+            2 => "Credit Card", 
+            3 => "Date",
+            _ => "Plain Text",
+        }
+    }
+
+    fn has_formatter(&self) -> bool {
+        self.editor.current_field() < 5 // First 5 fields have formatters
+    }
+
+    fn get_input_rules(&self) -> &'static str {
+        match self.editor.current_field() {
+            0 => "5 digits only (PSC format)",
+            1 => "10+ digits (US phone format)",
+            2 => "16+ digits (credit card)",
+            3 => "Digits as cents (12345 = $123.45)",
+            4 => "8 digits MMDDYYYY (date format)",
+            _ => "Any text (no formatting)",
+        }
+    }
+
+    fn cycle_example_data(&mut self) {
+        let examples = [
+            // PSC examples
+            vec!["01001", "1234567890", "1234567890123456", "12345", "12012024", "Plain text here"],
+            // Incomplete examples
+            vec!["010", "123", "1234", "123", "1201", "More text"],
+            // Invalid examples (will show error handling)
+            vec!["0abc1", "12a45", "123abc", "abc", "ab01cd", "Special chars!"],
+            // Edge cases
+            vec!["00000", "0000000000", "0000000000000000", "99", "13012024", ""],
+        ];
+        
+        self.example_mode = (self.example_mode + 1) % examples.len();
+        let current_examples = &examples[self.example_mode];
+        
+        for (i, example) in current_examples.iter().enumerate() {
+            if i < self.editor.data_provider().field_count() {
+                self.editor.data_provider_mut().set_field_value(i, example.to_string());
+            }
+        }
+        
+        let mode_names = ["Valid Examples", "Incomplete Input", "Invalid Characters", "Edge Cases"];
+        self.debug_message = format!("📋 Loaded: {}", mode_names[self.example_mode]);
+    }
+
+    // Enhanced status methods
+    fn toggle_validation(&mut self) {
+        self.validation_enabled = !self.validation_enabled;
+        self.editor.set_validation_enabled(self.validation_enabled);
+        self.debug_message = if self.validation_enabled {
+            "✅ Custom Formatters ENABLED".to_string()
+        } else {
+            "❌ Custom Formatters DISABLED".to_string()
+        };
+    }
+
+    fn toggle_raw_data_view(&mut self) {
+        self.show_raw_data = !self.show_raw_data;
+        self.debug_message = if self.show_raw_data {
+            "👁️ Showing RAW data focus".to_string()
+        } else {
+            "✨ Showing FORMATTED display focus".to_string()
+        };
+    }
+
+    fn toggle_cursor_details(&mut self) {
+        self.show_cursor_details = !self.show_cursor_details;
+        self.debug_message = if self.show_cursor_details {
+            "📍 Detailed cursor mapping info ON".to_string()
+        } else {
+            "📍 Detailed cursor mapping info OFF".to_string()
+        };
+    }
+
+    fn get_current_field_analysis(&self) -> (String, String, String, Option<String>) {
+        let raw = self.editor.current_text();
+        let display = self.editor.current_display_text();
+        
+        let status = if raw == display {
+            if self.has_formatter() {
+                if self.mode() == AppMode::Edit {
+                    "Raw (editing)".to_string()
+                } else {
+                    "No formatting needed".to_string()
+                }
+            } else {
+                "No formatter".to_string()
+            }
+        } else {
+            "Custom formatted".to_string()
+        };
+
+        let warning = if self.validation_enabled && self.has_formatter() {
+            // Check if there are any formatting warnings
+            if raw.len() > 0 {
+                match self.editor.current_field() {
+                    0 if raw.len() < 5 => Some(format!("PSC incomplete: {}/5", raw.len())),
+                    1 if raw.len() < 10 => Some(format!("Phone incomplete: {}/10", raw.len())),
+                    2 if raw.len() < 16 => Some(format!("Card incomplete: {}/16", raw.len())),
+                    4 if raw.len() < 8 => Some(format!("Date incomplete: {}/8", raw.len())),
+                    _ => None,
+                }
+            } else {
+                None
+            }
+        } else {
+            None
+        };
+
+        (raw.to_string(), display, status, warning)
+    }
+
+    // Delegate methods with enhanced feedback
+    fn enter_edit_mode(&mut self) {
+        self.editor.enter_edit_mode();
+        let field_type = self.current_field_type();
+        let rules = self.get_input_rules();
+        self.debug_message = format!("✏️ EDITING {} - {}", field_type, rules);
+    }
+
+    fn exit_edit_mode(&mut self) {
+        self.editor.exit_edit_mode();
+        let (raw, display, _, warning) = self.get_current_field_analysis();
+        if let Some(warn) = warning {
+            self.debug_message = format!("🔒 NORMAL - {} | ⚠️ {}", self.current_field_type(), warn);
+        } else if raw != display {
+            self.debug_message = format!("🔒 NORMAL - {} formatted successfully", self.current_field_type());
+        } else {
+            self.debug_message = "🔒 NORMAL MODE".to_string();
+        }
+    }
+
+    fn insert_char(&mut self, ch: char) -> anyhow::Result<()> {
+        let result = self.editor.insert_char(ch);
+        if result.is_ok() {
+            let (raw, display, _, _) = self.get_current_field_analysis();
+            if raw != display && self.validation_enabled {
+                self.debug_message = format!("✏️ '{}' added - Real-time formatting active", ch);
+            } else {
+                self.debug_message = format!("✏️ '{}' added", ch);
+            }
+        }
+        result
+    }
+
+    // Position mapping demo
+    fn show_position_mapping(&mut self) {
+        if !self.has_formatter() {
+            self.debug_message = "📍 No position mapping (plain text field)".to_string();
+            return;
+        }
+
+        let raw_pos = self.editor.cursor_position();
+        let display_pos = self.editor.display_cursor_position();
+        let raw = self.editor.current_text();
+        let display = self.editor.current_display_text();
+        
+        if raw_pos != display_pos {
+            self.debug_message = format!(
+                "🗺️ Position mapping: Raw[{}]='{}' ↔ Display[{}]='{}'",
+                raw_pos,
+                raw.chars().nth(raw_pos).unwrap_or('∅'),
+                display_pos,
+                display.chars().nth(display_pos).unwrap_or('∅')
+            );
+        } else {
+            self.debug_message = format!("📍 Cursor at position {} (no mapping needed)", raw_pos);
+        }
+    }
+
+    // Delegate remaining methods
+    fn mode(&self) -> AppMode { self.editor.mode() }
+    fn current_field(&self) -> usize { self.editor.current_field() }
+    fn cursor_position(&self) -> usize { self.editor.cursor_position() }
+    fn data_provider(&self) -> &D { self.editor.data_provider() }
+    fn data_provider_mut(&mut self) -> &mut D { self.editor.data_provider_mut() }
+    fn ui_state(&self) -> &canvas::EditorState { self.editor.ui_state() }
+    
+    fn move_up(&mut self) { let _ = self.editor.move_up(); }
+    fn move_down(&mut self) { let _ = self.editor.move_down(); }
+    fn move_left(&mut self) { let _ = self.editor.move_left(); }
+    fn move_right(&mut self) { let _ = self.editor.move_right(); }
+    fn delete_backward(&mut self) -> anyhow::Result<()> { self.editor.delete_backward() }
+    fn delete_forward(&mut self) -> anyhow::Result<()> { self.editor.delete_forward() }
+    fn next_field(&mut self) { let _ = self.editor.next_field(); }
+    fn prev_field(&mut self) { let _ = self.editor.prev_field(); }
+}
+
+// Enhanced key handling
+fn handle_key_press(
+    key: KeyCode,
+    modifiers: KeyModifiers,
+    editor: &mut EnhancedDemoEditor<MultiFormatterDemoData>,
+) -> anyhow::Result<bool> {
+    let mode = editor.mode();
+
+    // Quit
+    if matches!(key, KeyCode::F(10)) || 
+       (key == KeyCode::Char('q') && modifiers.contains(KeyModifiers::CONTROL)) ||
+       (key == KeyCode::Char('c') && modifiers.contains(KeyModifiers::CONTROL)) {
+        return Ok(false);
+    }
+
+    match (mode, key, modifiers) {
+        // Mode transitions
+        (AppMode::ReadOnly, KeyCode::Char('i'), _) => editor.enter_edit_mode(),
+        (AppMode::ReadOnly, KeyCode::Char('a'), _) => {
+            editor.editor.enter_append_mode();
+            editor.debug_message = format!("✏️ APPEND {} - {}", editor.current_field_type(), editor.get_input_rules());
+        },
+        (_, KeyCode::Esc, _) => editor.exit_edit_mode(),
+
+        // Enhanced demo features
+        (AppMode::ReadOnly, KeyCode::Char('e'), _) => editor.cycle_example_data(),
+        (AppMode::ReadOnly, KeyCode::Char('r'), _) => editor.toggle_raw_data_view(),
+        (AppMode::ReadOnly, KeyCode::Char('c'), _) => editor.toggle_cursor_details(),
+        (AppMode::ReadOnly, KeyCode::Char('m'), _) => editor.show_position_mapping(),
+        (AppMode::ReadOnly, KeyCode::F(1), _) => editor.toggle_validation(),
+
+        // Movement
+        (_, KeyCode::Up, _) | (AppMode::ReadOnly, KeyCode::Char('k'), _) => editor.move_up(),
+        (_, KeyCode::Down, _) | (AppMode::ReadOnly, KeyCode::Char('j'), _) => editor.move_down(),
+        (_, KeyCode::Left, _) | (AppMode::ReadOnly, KeyCode::Char('h'), _) => editor.move_left(),
+        (_, KeyCode::Right, _) | (AppMode::ReadOnly, KeyCode::Char('l'), _) => editor.move_right(),
+        (_, KeyCode::Tab, _) => editor.next_field(),
+        (_, KeyCode::BackTab, _) => editor.prev_field(),
+
+        // Editing
+        (AppMode::Edit, KeyCode::Char(c), m) if !m.contains(KeyModifiers::CONTROL) => {
+            editor.insert_char(c)?;
+        },
+        (AppMode::Edit, KeyCode::Backspace, _) => { editor.delete_backward()?; },
+        (AppMode::Edit, KeyCode::Delete, _) => { editor.delete_forward()?; },
+
+        // Field analysis
+        (AppMode::ReadOnly, KeyCode::Char('?'), _) => {
+            let (raw, display, status, warning) = editor.get_current_field_analysis();
+            let warning_text = warning.map(|w| format!(" ⚠️ {}", w)).unwrap_or_default();
+            editor.debug_message = format!(
+                "🔍 Field {}: {} | Raw: '{}' | Display: '{}'{}", 
+                editor.current_field() + 1, status, raw, display, warning_text
+            );
+        },
+
+        _ => {}
+    }
+
+    Ok(true)
+}
+
+fn run_app<B: Backend>(
+    terminal: &mut Terminal<B>,
+    mut editor: EnhancedDemoEditor<MultiFormatterDemoData>,
+) -> io::Result<()> {
+    loop {
+        terminal.draw(|f| ui(f, &editor))?;
+
+        if let Event::Key(key) = event::read()? {
+            match handle_key_press(key.code, key.modifiers, &mut editor) {
+                Ok(should_continue) => {
+                    if !should_continue {
+                        break;
+                    }
+                }
+                Err(e) => {
+                    editor.debug_message = format!("❌ Error: {}", e);
+                }
+            }
+        }
+    }
+    Ok(())
+}
+
+fn ui(f: &mut Frame, editor: &EnhancedDemoEditor<MultiFormatterDemoData>) {
+    let chunks = Layout::default()
+        .direction(Direction::Vertical)
+        .constraints([Constraint::Min(8), Constraint::Length(18)])
+        .split(f.area());
+
+    render_canvas_default(f, chunks[0], &editor.editor);
+    render_enhanced_status(f, chunks[1], editor);
+}
+
+fn render_enhanced_status(
+    f: &mut Frame,
+    area: Rect,
+    editor: &EnhancedDemoEditor<MultiFormatterDemoData>,
+) {
+    let chunks = Layout::default()
+        .direction(Direction::Vertical)
+        .constraints([
+            Constraint::Length(3),  // Status bar
+            Constraint::Length(6),  // Current field analysis
+            Constraint::Length(9),  // Help
+        ])
+        .split(area);
+
+    // Status bar
+    let mode_text = match editor.mode() {
+        AppMode::Edit => "INSERT",
+        AppMode::ReadOnly => "NORMAL",
+        _ => "OTHER",
+    };
+
+    let formatter_count = (0..editor.data_provider().field_count())
+        .filter(|&i| editor.data_provider().validation_config(i).is_some())
+        .count();
+
+    let status_text = format!(
+        "-- {} -- {} | Formatters: {}/{} active | View: {}{}",
+        mode_text,
+        editor.debug_message,
+        formatter_count,
+        editor.data_provider().field_count(),
+        if editor.show_raw_data { "RAW" } else { "DISPLAY" },
+        if editor.show_cursor_details { " | CURSOR+" } else { "" }
+    );
+
+    let status = Paragraph::new(Line::from(Span::raw(status_text)))
+        .block(Block::default().borders(Borders::ALL).title("🧩 Enhanced Custom Formatter Demo"));
+
+    f.render_widget(status, chunks[0]);
+
+    // Current field analysis
+    let (raw, display, status, warning) = editor.get_current_field_analysis();
+    let field_name = editor.data_provider().field_name(editor.current_field());
+    let field_type = editor.current_field_type();
+    
+    let mut analysis_lines = vec![
+        format!("📝 Current: {} ({})", field_name, field_type),
+        format!("🔧 Status: {}", status),
+    ];
+
+    if editor.show_raw_data || editor.mode() == AppMode::Edit {
+        analysis_lines.push(format!("💾 Raw Data: '{}'", raw));
+        analysis_lines.push(format!("✨ Display: '{}'", display));
+    } else {
+        analysis_lines.push(format!("✨ User Sees: '{}'", display));
+        analysis_lines.push(format!("💾 Stored As: '{}'", raw));
+    }
+
+    if editor.show_cursor_details {
+        analysis_lines.push(format!(
+            "📍 Cursor: Raw[{}] → Display[{}]",
+            editor.cursor_position(),
+            editor.editor.display_cursor_position()
+        ));
+    }
+
+    if let Some(ref warn) = warning {
+        analysis_lines.push(format!("⚠️ Warning: {}", warn));
+    }
+
+    let analysis_color = if warning.is_some() {
+        Color::Yellow
+    } else if raw != display && editor.validation_enabled {
+        Color::Green
+    } else {
+        Color::Gray
+    };
+
+    let analysis = Paragraph::new(analysis_lines.join("\n"))
+        .block(Block::default().borders(Borders::ALL).title("🔍 Field Analysis"))
+        .style(Style::default().fg(analysis_color))
+        .wrap(Wrap { trim: true });
+
+    f.render_widget(analysis, chunks[1]);
+
+    // Enhanced help
+    let help_text = match editor.mode() {
+        AppMode::ReadOnly => {
+            "🧩 ENHANCED CUSTOM FORMATTER DEMO\n\
+             \n\
+             Try these formatters:
+             • PSC: 01001 → 010 01 | Phone: 1234567890 → (123) 456-7890 | Card: 1234567890123456 → 1234 5678 9012 3456
+             • Date: 12012024 → 12/01/2024 | Plain: no formatting
+             \n\
+             Commands: i=insert, e=cycle examples, r=toggle raw/display, c=cursor details, m=position mapping\n\
+             Movement: hjkl/arrows, Tab=next field, ?=analyze current field, F1=toggle formatters\n\
+             Ctrl+C/F10=quit"
+        }
+        AppMode::Edit => {
+            "✏️ INSERT MODE - Real-time formatting as you type!\n\
+             \n\
+             Current field rules: {}\n\
+             • Raw input is authoritative (what gets stored)\n\
+             • Display formatting updates in real-time (what users see)\n\
+             • Cursor position is mapped between raw and display\n\
+             \n\
+             Esc=normal mode, arrows=navigate, Backspace/Del=delete"
+        }
+        _ => "🧩 Enhanced Custom Formatter Demo"
+    };
+
+    let formatted_help = if editor.mode() == AppMode::Edit {
+        help_text.replace("{}", editor.get_input_rules())
+    } else {
+        help_text.to_string()
+    };
+
+    let help = Paragraph::new(formatted_help)
+        .block(Block::default().borders(Borders::ALL).title("🚀 Enhanced Features & Commands"))
+        .style(Style::default().fg(Color::Gray))
+        .wrap(Wrap { trim: true });
+
+    f.render_widget(help, chunks[2]);
+}
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    println!("🧩 Enhanced Canvas Custom Formatter Demo (Feature 4)");
+    println!("✅ validation feature: ENABLED");
+    println!("✅ gui feature: ENABLED");
+    println!("🧩 Enhanced features:");
+    println!("   • 5 different custom formatters with edge cases");
+    println!("   • Real-time format preview and validation");
+    println!("   • Advanced cursor position mapping");
+    println!("   • Comprehensive error handling and warnings");
+    println!("   • Raw vs formatted data separation demos");
+    println!();
+
+    enable_raw_mode()?;
+    let mut stdout = io::stdout();
+    execute!(stdout, EnterAlternateScreen, EnableMouseCapture)?;
+    let backend = CrosstermBackend::new(stdout);
+    let mut terminal = Terminal::new(backend)?;
+
+    let data = MultiFormatterDemoData::new();
+    let editor = EnhancedDemoEditor::new(data);
+
+    let res = run_app(&mut terminal, editor);
+
+    disable_raw_mode()?;
+    execute!(terminal.backend_mut(), LeaveAlternateScreen, DisableMouseCapture)?;
+    terminal.show_cursor()?;
+
+    if let Err(err) = res {
+        println!("{:?}", err);
+    }
+
+    println!("🧩 Enhanced custom formatter demo completed!");
+    println!("🏆 You experienced comprehensive custom formatting with:");
+    println!("   • Multiple formatter types (PSC, Phone, Credit Card, Date)");
+    println!("   • Edge case handling (incomplete, invalid, overflow)");
+    println!("   • Real-time format preview and cursor mapping");
+    println!("   • Clear separation between raw business data and display formatting");
+    Ok(())
+}

canvas/src/autocomplete/mod.rs

@@ -1,12 +0,0 @@
-// src/autocomplete/mod.rs
-
-pub mod state;
-#[cfg(feature = "gui")]
-pub mod gui;
-
-// Re-export the main autocomplete types
-pub use state::{AutocompleteProvider, SuggestionItem};
-
-// Re-export GUI functions if available
-#[cfg(feature = "gui")]
-pub use gui::render_autocomplete_dropdown;

canvas/src/autocomplete/state.rs

@@ -1,5 +0,0 @@
-// src/autocomplete/state.rs
-//! Autocomplete provider types
-
-// Re-export the main types from data_provider
-pub use crate::data_provider::{AutocompleteProvider, SuggestionItem};

canvas/src/canvas/actions/types.rs

@@ -30,12 +30,12 @@ pub enum CanvasAction {
     DeleteBackward,
     DeleteForward,
 
-    // Autocomplete actions
+    // Suggestions actions
-    TriggerAutocomplete,
+        TriggerSuggestions,
-    SuggestionUp,
+        SuggestionUp,
-    SuggestionDown,
+        SuggestionDown,
-    SelectSuggestion,
+        SelectSuggestion,
-    ExitSuggestions,
+        ExitSuggestions,
 
     // Custom actions
     Custom(String),
@@ -101,7 +101,7 @@ impl CanvasAction {
             Self::InsertChar(_c) => "insert character",
             Self::DeleteBackward => "delete backward",
             Self::DeleteForward => "delete forward",
-            Self::TriggerAutocomplete => "trigger autocomplete",
+            Self::TriggerSuggestions => "trigger suggestions",
             Self::SuggestionUp => "suggestion up",
             Self::SuggestionDown => "suggestion down",
             Self::SelectSuggestion => "select suggestion",
@@ -139,10 +139,10 @@ impl CanvasAction {
         ]
     }
 
-    /// Get all autocomplete-related actions
+    /// Get all suggestions-related actions
-    pub fn autocomplete_actions() -> Vec<CanvasAction> {
+    pub fn suggestions_actions() -> Vec<CanvasAction> {
         vec![
-            Self::TriggerAutocomplete,
+            Self::TriggerSuggestions,
             Self::SuggestionUp,
             Self::SuggestionDown,
             Self::SelectSuggestion,

canvas/src/canvas/gui.rs

@@ -19,7 +19,7 @@ use crate::editor::FormEditor;
 #[cfg(feature = "gui")]
 use std::cmp::{max, min};
 
-/// Render ONLY the canvas form fields - no autocomplete
+/// Render ONLY the canvas form fields - no suggestions rendering here
 /// Updated to work with FormEditor instead of CanvasState trait
 #[cfg(feature = "gui")]
 pub fn render_canvas<T: CanvasTheme, D: DataProvider>(
@@ -53,24 +53,10 @@ pub fn render_canvas_with_highlight<T: CanvasTheme, D: DataProvider>(
     for i in 0..field_count {
         fields.push(data_provider.field_name(i));
 
-        // Use display text that applies masks if configured
+        // Use editor-provided effective display text per field (Feature 4/mask aware)
         #[cfg(feature = "validation")]
         {
-            if i == editor.current_field() {
+            inputs.push(editor.display_text_for_field(i));
-                inputs.push(editor.current_display_text());
-            } else {
-                // For non-current fields, we need to apply mask manually
-                let raw = data_provider.field_value(i);
-                if let Some(cfg) = editor.ui_state().validation_state().get_field_config(i) {
-                    if let Some(mask) = &cfg.display_mask {
-                        inputs.push(mask.apply_to_display(raw));
-                    } else {
-                        inputs.push(raw.to_string());
-                    }
-                } else {
-                    inputs.push(raw.to_string());
-                }
-            }
         }
         #[cfg(not(feature = "validation"))]
         {
@@ -93,23 +79,10 @@ pub fn render_canvas_with_highlight<T: CanvasTheme, D: DataProvider>(
         editor.display_cursor_position(), // Use display cursor position for masks
         false, // TODO: track unsaved changes in editor
         |i| {
-            // Get display value for field i
+            // Get display value for field i using editor logic (Feature 4 + masks)
             #[cfg(feature = "validation")]
             {
-                if i == editor.current_field() {
+                editor.display_text_for_field(i)
-                    editor.current_display_text()
-                } else {
-                    let raw = data_provider.field_value(i);
-                    if let Some(cfg) = editor.ui_state().validation_state().get_field_config(i) {
-                        if let Some(mask) = &cfg.display_mask {
-                            mask.apply_to_display(raw)
-                        } else {
-                            raw.to_string()
-                        }
-                    } else {
-                        raw.to_string()
-                    }
-                }
             }
             #[cfg(not(feature = "validation"))]
             {
@@ -117,12 +90,21 @@ pub fn render_canvas_with_highlight<T: CanvasTheme, D: DataProvider>(
             }
         },
         |i| {
-            // Check if field has display override (mask)
+            // Check if field has display override (custom formatter or mask)
             #[cfg(feature = "validation")]
             {
                 editor.ui_state().validation_state().get_field_config(i)
-                    .and_then(|cfg| cfg.display_mask.as_ref())
+                    .map(|cfg| {
-                    .is_some()
+                        // Formatter takes precedence; if present, it's a display override
+                        #[allow(unused_mut)]
+                        let mut has_override = false;
+                        #[cfg(feature = "validation")]
+                        {
+                            has_override = cfg.custom_formatter.is_some();
+                        }
+                        has_override || cfg.display_mask.is_some()
+                    })
+                    .unwrap_or(false)
             }
             #[cfg(not(feature = "validation"))]
             {

canvas/src/canvas/state.rs

@@ -14,8 +14,8 @@ pub struct EditorState {
     // Mode state
     pub(crate) current_mode: AppMode,
 
-    // Autocomplete state
+    // Suggestions dropdown state
-    pub(crate) autocomplete: AutocompleteUIState,
+    pub(crate) suggestions: SuggestionsUIState,
 
     // Selection state (for vim visual mode)
     pub(crate) selection: SelectionState,
@@ -26,7 +26,7 @@ pub struct EditorState {
 }
 
 #[derive(Debug, Clone)]
-pub struct AutocompleteUIState {
+pub struct SuggestionsUIState {
     pub(crate) is_active: bool,
     pub(crate) is_loading: bool,
     pub(crate) selected_index: Option<usize>,
@@ -47,7 +47,7 @@ impl EditorState {
             cursor_pos: 0,
             ideal_cursor_column: 0,
             current_mode: AppMode::Edit,
-            autocomplete: AutocompleteUIState {
+            suggestions: SuggestionsUIState {
                 is_active: false,
                 is_loading: false,
                 selected_index: None,
@@ -83,14 +83,14 @@ impl EditorState {
         self.current_mode
     }
 
-    /// Check if autocomplete is active (for user's business logic)
+    /// Check if suggestions dropdown is active (for user's business logic)
-    pub fn is_autocomplete_active(&self) -> bool {
+    pub fn is_suggestions_active(&self) -> bool {
-        self.autocomplete.is_active
+        self.suggestions.is_active
     }
 
-    /// Check if autocomplete is loading (for user's business logic)
+    /// Check if suggestions dropdown is loading (for user's business logic)
-    pub fn is_autocomplete_loading(&self) -> bool {
+    pub fn is_suggestions_loading(&self) -> bool {
-        self.autocomplete.is_loading
+        self.suggestions.is_loading
     }
 
     /// Get selection state (for user's business logic)
@@ -128,18 +128,18 @@ impl EditorState {
         self.ideal_cursor_column = self.cursor_pos;
     }
 
-    pub(crate) fn activate_autocomplete(&mut self, field_index: usize) {
+    pub(crate) fn activate_suggestions(&mut self, field_index: usize) {
-        self.autocomplete.is_active = true;
+        self.suggestions.is_active = true;
-        self.autocomplete.is_loading = true;
+        self.suggestions.is_loading = true;
-        self.autocomplete.active_field = Some(field_index);
+        self.suggestions.active_field = Some(field_index);
-        self.autocomplete.selected_index = None;
+        self.suggestions.selected_index = None;
     }
 
-    pub(crate) fn deactivate_autocomplete(&mut self) {
+    pub(crate) fn deactivate_suggestions(&mut self) {
-        self.autocomplete.is_active = false;
+        self.suggestions.is_active = false;
-        self.autocomplete.is_loading = false;
+        self.suggestions.is_loading = false;
-        self.autocomplete.active_field = None;
+        self.suggestions.active_field = None;
-        self.autocomplete.selected_index = None;
+        self.suggestions.selected_index = None;
     }
 }
 

canvas/src/data_provider.rs

@@ -18,8 +18,8 @@ pub trait DataProvider {
     /// Set field value (library calls this when text changes)
     fn set_field_value(&mut self, index: usize, value: String);
 
-    /// Check if field supports autocomplete (optional)
+    /// Check if field supports suggestions (optional)
-    fn supports_autocomplete(&self, _field_index: usize) -> bool {
+    fn supports_suggestions(&self, _field_index: usize) -> bool {
         false
     }
 
@@ -36,10 +36,10 @@ pub trait DataProvider {
     }
 }
 
-/// Optional: User implements this for autocomplete data
+/// Optional: User implements this for suggestions data
 #[async_trait]
-pub trait AutocompleteProvider {
+pub trait SuggestionsProvider {
-    /// Fetch autocomplete suggestions (user's business logic)
+    /// Fetch suggestions (user's business logic)
     async fn fetch_suggestions(&mut self, field_index: usize, query: &str)
         -> Result<Vec<SuggestionItem>>;
 }

canvas/src/editor.rs

@@ -7,7 +7,7 @@ use crate::canvas::CursorManager;
 
 use anyhow::Result;
 use crate::canvas::state::EditorState;
-use crate::data_provider::{DataProvider, AutocompleteProvider, SuggestionItem};
+use crate::data_provider::{DataProvider, SuggestionsProvider, SuggestionItem};
 use crate::canvas::modes::AppMode;
 use crate::canvas::state::SelectionState;
 
@@ -70,9 +70,9 @@ impl<D: DataProvider> FormEditor<D> {
         self.ui_state.mode()
     }
 
-    /// Check if autocomplete is active (for user's logic)
+    /// Check if suggestions dropdown is active (for user's logic)
-    pub fn is_autocomplete_active(&self) -> bool {
+    pub fn is_suggestions_active(&self) -> bool {
-        self.ui_state.is_autocomplete_active()
+        self.ui_state.is_suggestions_active()
     }
 
     /// Get current field text (convenience method)
@@ -85,7 +85,14 @@ impl<D: DataProvider> FormEditor<D> {
         }
     }
 
-    /// Get current field text for display, applying mask if configured
+    /// Get current field text for display.
+    ///
+    /// Policies:
+    /// - Feature 4 (custom formatter):
+    ///   - While editing the focused field: ALWAYS show raw (no custom formatting).
+    ///   - When not editing the field: show formatted (fallback to raw on error).
+    /// - Mask-only fields: mask applies even in Edit mode (preserve legacy behavior).
+    /// - Otherwise: raw.
     #[cfg(feature = "validation")]
     pub fn current_display_text(&self) -> String {
         let field_index = self.ui_state.current_field;
@@ -96,10 +103,29 @@ impl<D: DataProvider> FormEditor<D> {
         };
 
         if let Some(cfg) = self.ui_state.validation.get_field_config(field_index) {
+            // 1) Mask-only fields: mask applies even in Edit (legacy behavior)
+            if cfg.custom_formatter.is_none() {
+                if let Some(mask) = &cfg.display_mask {
+                    return mask.apply_to_display(raw);
+                }
+            }
+
+            // 2) Feature 4 fields: raw while editing, formatted otherwise
+            if cfg.custom_formatter.is_some() {
+                if matches!(self.ui_state.current_mode, AppMode::Edit) {
+                    return raw.to_string();
+                }
+                if let Some((formatted, _mapper, _warning)) = cfg.run_custom_formatter(raw) {
+                    return formatted;
+                }
+            }
+
+            // 3) Fallback to mask if present (when formatter didn't produce output)
             if let Some(mask) = &cfg.display_mask {
                 return mask.apply_to_display(raw);
             }
         }
+
         raw.to_string()
     }
 
@@ -108,6 +134,71 @@ impl<D: DataProvider> FormEditor<D> {
         &self.ui_state
     }
 
+    /// Set external validation state for a field (Feature 5)
+    #[cfg(feature = "validation")]
+    pub fn set_external_validation(
+        &mut self,
+        field_index: usize,
+        state: crate::validation::ExternalValidationState,
+    ) {
+        self.ui_state
+            .validation
+            .set_external_validation(field_index, state);
+    }
+
+    /// Clear external validation state for a field (Feature 5)
+    #[cfg(feature = "validation")]
+    pub fn clear_external_validation(&mut self, field_index: usize) {
+        self.ui_state.validation.clear_external_validation(field_index);
+    }
+
+    /// Get effective display text for any field index.
+    ///
+    /// Policies:
+    /// - Feature 4 fields (with custom formatter):
+    ///   - If the field is currently focused AND in Edit mode: return raw (no formatting).
+    ///   - Otherwise: return formatted (fallback to raw on error).
+    /// - Mask-only fields: mask applies regardless of mode (legacy behavior).
+    /// - Otherwise: raw.
+    #[cfg(feature = "validation")]
+    pub fn display_text_for_field(&self, field_index: usize) -> String {
+        let raw = if field_index < self.data_provider.field_count() {
+            self.data_provider.field_value(field_index)
+        } else {
+            ""
+        };
+
+        if let Some(cfg) = self.ui_state.validation.get_field_config(field_index) {
+            // Mask-only fields: mask applies even in Edit mode
+            if cfg.custom_formatter.is_none() {
+                if let Some(mask) = &cfg.display_mask {
+                    return mask.apply_to_display(raw);
+                }
+            }
+
+            // Feature 4 fields:
+            if cfg.custom_formatter.is_some() {
+                // Focused + Edit -> raw
+                if field_index == self.ui_state.current_field
+                    && matches!(self.ui_state.current_mode, AppMode::Edit)
+                {
+                    return raw.to_string();
+                }
+                // Not editing -> formatted
+                if let Some((formatted, _mapper, _warning)) = cfg.run_custom_formatter(raw) {
+                    return formatted;
+                }
+            }
+
+            // Fallback to mask if present (in case formatter didn't return output)
+            if let Some(mask) = &cfg.display_mask {
+                return mask.apply_to_display(raw);
+            }
+        }
+
+        raw.to_string()
+    }
+
     /// Get reference to data provider for rendering
     pub fn data_provider(&self) -> &D {
         &self.data_provider
@@ -489,50 +580,51 @@ impl<D: DataProvider> FormEditor<D> {
     }
 
     // ===================================================================
-    // ASYNC OPERATIONS: Only autocomplete needs async
+    // ASYNC OPERATIONS: Only suggestions need async
     // ===================================================================
 
-    /// Trigger autocomplete (async because it fetches data)
+    /// Trigger suggestions (async because it fetches data)
-    pub async fn trigger_autocomplete<A>(&mut self, provider: &mut A) -> Result<()>
+    pub async fn trigger_suggestions<A>(&mut self, provider: &mut A) -> Result<()>
     where
-        A: AutocompleteProvider,
+        A: SuggestionsProvider,
     {
         let field_index = self.ui_state.current_field;
 
-        if !self.data_provider.supports_autocomplete(field_index) {
+        if !self.data_provider.supports_suggestions(field_index) {
             return Ok(());
         }
 
-        // Activate autocomplete UI
+        // Activate suggestions UI
-        self.ui_state.activate_autocomplete(field_index);
+        self.ui_state.activate_suggestions(field_index);
 
         // Fetch suggestions from user (no conversion needed!)
         let query = self.current_text();
         self.suggestions = provider.fetch_suggestions(field_index, query).await?;
 
         // Update UI state
-        self.ui_state.autocomplete.is_loading = false;
+        self.ui_state.suggestions.is_loading = false;
         if !self.suggestions.is_empty() {
-            self.ui_state.autocomplete.selected_index = Some(0);
+            self.ui_state.suggestions.selected_index = Some(0);
         }
 
         Ok(())
     }
 
-    /// Navigate autocomplete suggestions
+    /// Navigate suggestions
-    pub fn autocomplete_next(&mut self) {
+    pub fn suggestions_next(&mut self) {
-        if !self.ui_state.autocomplete.is_active || self.suggestions.is_empty() {
+        if !self.ui_state.suggestions.is_active || self.suggestions.is_empty() {
             return;
         }
 
-        let current = self.ui_state.autocomplete.selected_index.unwrap_or(0);
+        let current = self.ui_state.suggestions.selected_index.unwrap_or(0);
         let next = (current + 1) % self.suggestions.len();
-        self.ui_state.autocomplete.selected_index = Some(next);
+        self.ui_state.suggestions.selected_index = Some(next);
     }
 
-    /// Apply selected autocomplete suggestion
+    /// Apply selected suggestion
-    pub fn apply_autocomplete(&mut self) -> Option<String> {
+    /// Apply selected suggestion
-        if let Some(selected_index) = self.ui_state.autocomplete.selected_index {
+    pub fn apply_suggestion(&mut self) -> Option<String> {
+        if let Some(selected_index) = self.ui_state.suggestions.selected_index {
             if let Some(suggestion) = self.suggestions.get(selected_index).cloned() {
                 let field_index = self.ui_state.current_field;
 
@@ -546,8 +638,8 @@ impl<D: DataProvider> FormEditor<D> {
                 self.ui_state.cursor_pos = suggestion.value_to_store.len();
                 self.ui_state.ideal_cursor_column = self.ui_state.cursor_pos;
 
-                // Close autocomplete
+                // Close suggestions
-                self.ui_state.deactivate_autocomplete();
+                self.ui_state.deactivate_suggestions();
                 self.suggestions.clear();
 
                 // Validate the new content if validation is enabled
@@ -860,8 +952,8 @@ impl<D: DataProvider> FormEditor<D> {
         }
 
         self.set_mode(AppMode::ReadOnly);
-        // Deactivate autocomplete when exiting edit mode
+        // Deactivate suggestions when exiting edit mode
-        self.ui_state.deactivate_autocomplete();
+        self.ui_state.deactivate_suggestions();
 
         Ok(())
     }
@@ -959,7 +1051,7 @@ impl<D: DataProvider> FormEditor<D> {
         self.ui_state.ideal_cursor_column = clamped_pos;
     }
 
-    /// Get cursor position for display (maps raw cursor to display position with mask)
+    /// Get cursor position for display (maps raw cursor to display position with formatter/mask)
     pub fn display_cursor_position(&self) -> usize {
         let current_text = self.current_text();
         let raw_pos = match self.ui_state.current_mode {
@@ -977,6 +1069,13 @@ impl<D: DataProvider> FormEditor<D> {
         {
             let field_index = self.ui_state.current_field;
             if let Some(cfg) = self.ui_state.validation.get_field_config(field_index) {
+                // Only apply custom formatter cursor mapping when NOT editing
+                if !matches!(self.ui_state.current_mode, AppMode::Edit) {
+                    if let Some((formatted, mapper, _warning)) = cfg.run_custom_formatter(current_text) {
+                        return mapper.raw_to_formatted(current_text, &formatted, raw_pos);
+                    }
+                }
+                // Fallback to display mask
                 if let Some(mask) = &cfg.display_mask {
                     return mask.raw_pos_to_display_pos(self.ui_state.cursor_pos);
                 }

canvas/src/lib.rs

@@ -4,9 +4,9 @@ pub mod canvas;
 pub mod editor;
 pub mod data_provider;
 
-// Only include autocomplete module if feature is enabled
+// Only include suggestions module if feature is enabled
-#[cfg(feature = "autocomplete")]
+#[cfg(feature = "suggestions")]
-pub mod autocomplete;
+pub mod suggestions;
 
 // Only include validation module if feature is enabled
 #[cfg(feature = "validation")]
@@ -21,7 +21,7 @@ pub use canvas::CursorManager;
 
 // Main API exports
 pub use editor::FormEditor;
-pub use data_provider::{DataProvider, AutocompleteProvider, SuggestionItem};
+pub use data_provider::{DataProvider, SuggestionsProvider, SuggestionItem};
 
 // UI state (read-only access for users)
 pub use canvas::state::EditorState;
@@ -37,6 +37,8 @@ pub use validation::{
     CharacterLimits, ValidationConfigBuilder, ValidationState,
     ValidationSummary, PatternFilters, PositionFilter, PositionRange, CharacterFilter, 
     DisplayMask,  // Simple display mask instead of complex ReservedCharacters
+    // Feature 4: custom formatting exports
+    CustomFormatter, FormattingResult, PositionMapper, DefaultPositionMapper,
 };
 
 // Theming and GUI
@@ -49,5 +51,5 @@ pub use canvas::gui::render_canvas;
 #[cfg(feature = "gui")]
 pub use canvas::gui::render_canvas_default;
 
-#[cfg(all(feature = "gui", feature = "autocomplete"))]
+#[cfg(all(feature = "gui", feature = "suggestions"))]
-pub use autocomplete::gui::render_autocomplete_dropdown;
+pub use suggestions::gui::render_suggestions_dropdown;

canvas/src/suggestions/gui.rs

@@ -1,5 +1,5 @@
-// src/autocomplete/gui.rs
+// src/suggestions/gui.rs
-//! Autocomplete GUI updated to work with FormEditor
+//! Suggestions dropdown GUI (not inline autocomplete) updated to work with FormEditor
 
 #[cfg(feature = "gui")]
 use ratatui::{
@@ -17,9 +17,9 @@ use crate::editor::FormEditor;
 #[cfg(feature = "gui")]
 use unicode_width::UnicodeWidthStr;
 
-/// Render autocomplete dropdown for FormEditor - call this AFTER rendering canvas
+/// Render suggestions dropdown for FormEditor - call this AFTER rendering canvas
 #[cfg(feature = "gui")]
-pub fn render_autocomplete_dropdown<T: CanvasTheme, D: DataProvider>(
+pub fn render_suggestions_dropdown<T: CanvasTheme, D: DataProvider>(
     f: &mut Frame,
     frame_area: Rect,
     input_rect: Rect,
@@ -28,14 +28,14 @@ pub fn render_autocomplete_dropdown<T: CanvasTheme, D: DataProvider>(
 ) {
     let ui_state = editor.ui_state();
 
-    if !ui_state.is_autocomplete_active() {
+    if !ui_state.is_suggestions_active() {
         return;
     }
 
-    if ui_state.autocomplete.is_loading {
+    if ui_state.suggestions.is_loading {
         render_loading_indicator(f, frame_area, input_rect, theme);
     } else if !editor.suggestions().is_empty() {
-        render_suggestions_dropdown(f, frame_area, input_rect, theme, editor.suggestions(), ui_state.autocomplete.selected_index);
+        render_suggestions_dropdown_list(f, frame_area, input_rect, theme, editor.suggestions(), ui_state.suggestions.selected_index);
     }
 }
 
@@ -71,7 +71,7 @@ fn render_loading_indicator<T: CanvasTheme>(
 
 /// Show actual suggestions list
 #[cfg(feature = "gui")]
-fn render_suggestions_dropdown<T: CanvasTheme>(
+fn render_suggestions_dropdown_list<T: CanvasTheme>(
     f: &mut Frame,
     frame_area: Rect,
     input_rect: Rect,

canvas/src/suggestions/mod.rs

@@ -0,0 +1,12 @@
+// src/suggestions/mod.rs
+
+pub mod state;
+#[cfg(feature = "gui")]
+pub mod gui;
+
+// Re-export the main suggestion types
+pub use state::{SuggestionsProvider, SuggestionItem};
+
+// Re-export GUI functions if available
+#[cfg(feature = "gui")]
+pub use gui::render_suggestions_dropdown;

canvas/src/suggestions/state.rs

@@ -0,0 +1,5 @@
+// src/suggestions/state.rs
+//! Suggestions provider types (for dropdown suggestions, not real inline autocomplete)
+
+// Re-export the main types from data_provider
+pub use crate::data_provider::{SuggestionsProvider, SuggestionItem};

canvas/src/validation/config.rs

@@ -2,9 +2,12 @@
 //! Validation configuration types and builders
 
 use crate::validation::{CharacterLimits, PatternFilters, DisplayMask};
+#[cfg(feature = "validation")]
+use crate::validation::{CustomFormatter, FormattingResult, PositionMapper};
+use std::sync::Arc;
 
 /// Main validation configuration for a field
-#[derive(Debug, Clone, Default)]
+#[derive(Clone, Default)]
 pub struct ValidationConfig {
     /// Character limit configuration
     pub character_limits: Option<CharacterLimits>,
@@ -15,13 +18,203 @@ pub struct ValidationConfig {
     /// User-defined display mask for visual formatting
     pub display_mask: Option<DisplayMask>,
 
-    /// Future: Custom formatting
+    /// Optional: user-provided custom formatter (feature 4)
-    pub custom_formatting: Option<()>, // Placeholder for future implementation
+    #[cfg(feature = "validation")]
+    pub custom_formatter: Option<Arc<dyn CustomFormatter + Send + Sync>>,
+
+    /// Enable external validation indicator UI (feature 5)
+    pub external_validation_enabled: bool,
 
     /// Future: External validation
     pub external_validation: Option<()>, // Placeholder for future implementation
 }
 
+/// Manual Debug to avoid requiring Debug on dyn CustomFormatter
+impl std::fmt::Debug for ValidationConfig {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut ds = f.debug_struct("ValidationConfig");
+        ds.field("character_limits", &self.character_limits)
+          .field("pattern_filters", &self.pattern_filters)
+          .field("display_mask", &self.display_mask)
+          // Do not print the formatter itself to avoid requiring Debug
+          .field(
+              "custom_formatter",
+              &{
+                  #[cfg(feature = "validation")]
+                  {
+                      if self.custom_formatter.is_some() { &"Some(<CustomFormatter>)" } else { &"None" }
+                  }
+                  #[cfg(not(feature = "validation"))]
+                  {
+                      &"N/A"
+                  }
+              },
+          )
+          .field("external_validation_enabled", &self.external_validation_enabled)
+          .field("external_validation", &self.external_validation)
+          .finish()
+    }
+}
+
+// ✅ FIXED: Move function from struct definition to impl block
+impl ValidationConfig {
+    /// If a custom formatter is configured, run it and return the formatted text,
+    /// the position mapper and an optional warning message.
+    ///
+    /// Returns None when no custom formatter is configured.
+    #[cfg(feature = "validation")]
+    pub fn run_custom_formatter(
+        &self,
+        raw: &str,
+    ) -> Option<(String, Arc<dyn PositionMapper>, Option<String>)> {
+        let formatter = self.custom_formatter.as_ref()?;
+        match formatter.format(raw) {
+            FormattingResult::Success { formatted, mapper } => {
+                Some((formatted, mapper, None))
+            }
+            FormattingResult::Warning { formatted, message, mapper } => {
+                Some((formatted, mapper, Some(message)))
+            }
+            FormattingResult::Error { .. } => None, // Fall back to raw display
+        }
+    }
+
+    /// Create a new empty validation configuration
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Create a configuration with just character limits
+    pub fn with_max_length(max_length: usize) -> Self {
+        ValidationConfigBuilder::new()
+            .with_max_length(max_length)
+            .build()
+    }
+
+    /// Create a configuration with pattern filters
+    pub fn with_patterns(patterns: PatternFilters) -> Self {
+        ValidationConfigBuilder::new()
+            .with_pattern_filters(patterns)
+            .build()
+    }
+
+    /// Create a configuration with user-defined display mask
+    ///
+    /// # Examples
+    /// ```
+    /// use canvas::{ValidationConfig, DisplayMask};
+    ///
+    /// let phone_mask = DisplayMask::new("(###) ###-####", '#');
+    /// let config = ValidationConfig::with_mask(phone_mask);
+    /// ```
+    pub fn with_mask(mask: DisplayMask) -> Self {
+        ValidationConfigBuilder::new()
+            .with_display_mask(mask)
+            .build()
+    }
+
+    /// Validate a character insertion at a specific position (raw text space).
+    ///
+    /// Note: Display masks are visual-only and do not participate in validation.
+    /// Editor logic is responsible for skipping mask separator positions; here we
+    /// only validate the raw insertion against limits and patterns.
+    pub fn validate_char_insertion(
+        &self,
+        current_text: &str,
+        position: usize,
+        character: char,
+    ) -> ValidationResult {
+        // Character limits validation
+        if let Some(ref limits) = self.character_limits {
+            // ✅ FIXED: Explicit return type annotation
+            if let Some(result) = limits.validate_insertion(current_text, position, character) {
+                if !result.is_acceptable() {
+                    return result;
+                }
+            }
+        }
+
+        // Pattern filters validation
+        if let Some(ref patterns) = self.pattern_filters {
+            // ✅ FIXED: Explicit error handling
+            if let Err(message) = patterns.validate_char_at_position(position, character) {
+                return ValidationResult::error(message);
+            }
+        }
+
+        // Future: Add other validation types here
+
+        ValidationResult::Valid
+    }
+
+    /// Validate the current text content (raw text space)
+    pub fn validate_content(&self, text: &str) -> ValidationResult {
+        // Character limits validation
+        if let Some(ref limits) = self.character_limits {
+            // ✅ FIXED: Explicit return type annotation
+            if let Some(result) = limits.validate_content(text) {
+                if !result.is_acceptable() {
+                    return result;
+                }
+            }
+        }
+
+        // Pattern filters validation
+        if let Some(ref patterns) = self.pattern_filters {
+            // ✅ FIXED: Explicit error handling
+            if let Err(message) = patterns.validate_text(text) {
+                return ValidationResult::error(message);
+            }
+        }
+
+        // Future: Add other validation types here
+
+        ValidationResult::Valid
+    }
+
+    /// Check if any validation rules are configured
+    pub fn has_validation(&self) -> bool {
+        self.character_limits.is_some()
+            || self.pattern_filters.is_some()
+            || self.display_mask.is_some()
+            || {
+                #[cfg(feature = "validation")]
+                { self.custom_formatter.is_some() }
+                #[cfg(not(feature = "validation"))]
+                { false }
+            }
+    }
+
+    pub fn allows_field_switch(&self, text: &str) -> bool {
+        // Character limits validation
+        if let Some(ref limits) = self.character_limits {
+            // ✅ FIXED: Direct boolean return
+            if !limits.allows_field_switch(text) {
+                return false;
+            }
+        }
+
+        // Future: Add other validation types here
+
+        true
+    }
+
+    /// Get reason why field switching is blocked (if any)
+    pub fn field_switch_block_reason(&self, text: &str) -> Option<String> {
+        // Character limits validation
+        if let Some(ref limits) = self.character_limits {
+            // ✅ FIXED: Direct option return
+            if let Some(reason) = limits.field_switch_block_reason(text) {
+                return Some(reason);
+            }
+        }
+
+        // Future: Add other validation types here
+
+        None
+    }
+}
+
 /// Builder for creating validation configurations
 #[derive(Debug, Default)]
 pub struct ValidationConfigBuilder {
@@ -47,24 +240,24 @@ impl ValidationConfigBuilder {
     }
 
     /// Set user-defined display mask for visual formatting
-    /// 
+    ///
     /// # Examples
     /// ```
     /// use canvas::{ValidationConfigBuilder, DisplayMask};
-    /// 
+    ///
     /// // Phone number with dynamic formatting
     /// let phone_mask = DisplayMask::new("(###) ###-####", '#');
     /// let config = ValidationConfigBuilder::new()
     ///     .with_display_mask(phone_mask)
     ///     .build();
-    /// 
+    ///
-    /// // Date with template formatting  
+    /// // Date with template formatting
     /// let date_mask = DisplayMask::new("##/##/####", '#')
     ///     .with_template('_');
     /// let config = ValidationConfigBuilder::new()
     ///     .with_display_mask(date_mask)
     ///     .build();
-    /// 
+    ///
     /// // Custom business format
     /// let employee_id = DisplayMask::new("EMP-####-##", '#')
     ///     .with_template('•');
@@ -78,12 +271,30 @@ impl ValidationConfigBuilder {
         self
     }
 
+    /// Set optional custom formatter (feature 4)
+    #[cfg(feature = "validation")]
+    pub fn with_custom_formatter<F>(mut self, formatter: Arc<F>) -> Self
+    where
+        F: CustomFormatter + Send + Sync + 'static,
+    {
+        self.config.custom_formatter = Some(formatter);
+        // When custom formatter is present, it takes precedence over display mask.
+        self.config.display_mask = None;
+        self
+    }
+
     /// Set maximum number of characters (convenience method)
     pub fn with_max_length(mut self, max_length: usize) -> Self {
         self.config.character_limits = Some(CharacterLimits::new(max_length));
         self
     }
 
+    /// Enable or disable external validation indicator UI (feature 5)
+    pub fn with_external_validation_enabled(mut self, enabled: bool) -> Self {
+        self.config.external_validation_enabled = enabled;
+        self
+    }
+
     /// Build the final validation configuration
     pub fn build(self) -> ValidationConfig {
         self.config
@@ -134,131 +345,6 @@ impl ValidationResult {
     }
 }
 
-impl ValidationConfig {
-    /// Create a new empty validation configuration
-    pub fn new() -> Self {
-        Self::default()
-    }
-
-    /// Create a configuration with just character limits
-    pub fn with_max_length(max_length: usize) -> Self {
-        ValidationConfigBuilder::new()
-            .with_max_length(max_length)
-            .build()
-    }
-
-    /// Create a configuration with pattern filters
-    pub fn with_patterns(patterns: PatternFilters) -> Self {
-        ValidationConfigBuilder::new()
-            .with_pattern_filters(patterns)
-            .build()
-    }
-
-    /// Create a configuration with user-defined display mask
-    /// 
-    /// # Examples
-    /// ```
-    /// use canvas::{ValidationConfig, DisplayMask};
-    /// 
-    /// let phone_mask = DisplayMask::new("(###) ###-####", '#');
-    /// let config = ValidationConfig::with_mask(phone_mask);
-    /// ```
-    pub fn with_mask(mask: DisplayMask) -> Self {
-        ValidationConfigBuilder::new()
-            .with_display_mask(mask)
-            .build()
-    }
-
-    /// Validate a character insertion at a specific position (raw text space).
-    ///
-    /// Note: Display masks are visual-only and do not participate in validation.
-    /// Editor logic is responsible for skipping mask separator positions; here we
-    /// only validate the raw insertion against limits and patterns.
-    pub fn validate_char_insertion(
-        &self,
-        current_text: &str,
-        position: usize,
-        character: char,
-    ) -> ValidationResult {
-        // Character limits validation
-        if let Some(ref limits) = self.character_limits {
-            if let Some(result) = limits.validate_insertion(current_text, position, character) {
-                if !result.is_acceptable() {
-                    return result;
-                }
-            }
-        }
-
-        // Pattern filters validation
-        if let Some(ref patterns) = self.pattern_filters {
-            if let Err(message) = patterns.validate_char_at_position(position, character) {
-                return ValidationResult::error(message);
-            }
-        }
-
-        // Future: Add other validation types here
-
-        ValidationResult::Valid
-    }
-
-    /// Validate the current text content (raw text space)
-    pub fn validate_content(&self, text: &str) -> ValidationResult {
-        // Character limits validation
-        if let Some(ref limits) = self.character_limits {
-            if let Some(result) = limits.validate_content(text) {
-                if !result.is_acceptable() {
-                    return result;
-                }
-            }
-        }
-
-        // Pattern filters validation
-        if let Some(ref patterns) = self.pattern_filters {
-            if let Err(message) = patterns.validate_text(text) {
-                return ValidationResult::error(message);
-            }
-        }
-
-        // Future: Add other validation types here
-
-        ValidationResult::Valid
-    }
-
-    /// Check if any validation rules are configured
-    pub fn has_validation(&self) -> bool {
-        self.character_limits.is_some() 
-            || self.pattern_filters.is_some() 
-            || self.display_mask.is_some()
-    }
-
-    pub fn allows_field_switch(&self, text: &str) -> bool {
-        // Character limits validation
-        if let Some(ref limits) = self.character_limits {
-            if !limits.allows_field_switch(text) {
-                return false;
-            }
-        }
-
-        // Future: Add other validation types here
-
-        true
-    }
-
-    /// Get reason why field switching is blocked (if any)
-    pub fn field_switch_block_reason(&self, text: &str) -> Option<String> {
-        // Character limits validation
-        if let Some(ref limits) = self.character_limits {
-            if let Some(reason) = limits.field_switch_block_reason(text) {
-                return Some(reason);
-            }
-        }
-
-        // Future: Add other validation types here
-
-        None
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -268,7 +354,7 @@ mod tests {
         // User creates their own phone mask
         let phone_mask = DisplayMask::new("(###) ###-####", '#');
         let config = ValidationConfig::with_mask(phone_mask);
-        
+
         // has_validation should be true because mask is configured
         assert!(config.has_validation());
 

canvas/src/validation/formatting.rs

@@ -0,0 +1,217 @@
+/* canvas/src/validation/formatting.rs
+   Add new formatting module with CustomFormatter, PositionMapper, DefaultPositionMapper, and FormattingResult
+*/
+use std::sync::Arc;
+
+/// Bidirectional mapping between raw input positions and formatted display positions.
+///
+/// The library uses this to keep cursor/selection behavior intuitive when the UI
+/// shows a formatted transformation (e.g., "01001" -> "010 01") while the editor
+/// still stores raw text.
+pub trait PositionMapper: Send + Sync {
+    /// Map a raw cursor position to a formatted cursor position.
+    ///
+    /// raw_pos is an index into the raw text (0..=raw.len() in char positions).
+    /// Implementations should return a position within 0..=formatted.len() (in char positions).
+    fn raw_to_formatted(&self, raw: &str, formatted: &str, raw_pos: usize) -> usize;
+
+    /// Map a formatted cursor position to a raw cursor position.
+    ///
+    /// formatted_pos is an index into the formatted text (0..=formatted.len()).
+    /// Implementations should return a position within 0..=raw.len() (in char positions).
+    fn formatted_to_raw(&self, raw: &str, formatted: &str, formatted_pos: usize) -> usize;
+}
+
+/// A reasonable default mapper that works for "insert separators" style formatting,
+/// such as grouping digits or adding dashes/spaces.
+///
+/// Heuristic:
+/// - Treat letters and digits (is_alphanumeric) in the formatted string as user-entered characters
+///   corresponding to raw characters, in order.
+/// - Treat any non-alphanumeric characters as purely visual separators.
+/// - Raw positions are mapped by counting alphanumeric characters in the formatted string.
+/// - If the formatted contains fewer alphanumeric characters than the raw (shouldn't happen
+///   for plain grouping), we cap at the end of the formatted string.
+#[derive(Clone, Default)]
+pub struct DefaultPositionMapper;
+
+impl PositionMapper for DefaultPositionMapper {
+    fn raw_to_formatted(&self, raw: &str, formatted: &str, raw_pos: usize) -> usize {
+        // Convert to char indices for correctness in presence of UTF-8
+        let raw_len = raw.chars().count();
+        let clamped_raw_pos = raw_pos.min(raw_len);
+
+        // Count alphanumerics in formatted, find the index where we've seen `clamped_raw_pos` of them.
+        let mut seen_user_chars = 0usize;
+        for (idx, ch) in formatted.char_indices() {
+            if ch.is_alphanumeric() {
+                if seen_user_chars == clamped_raw_pos {
+                    // Cursor is positioned before this user character in the formatted view
+                    return idx;
+                }
+                seen_user_chars += 1;
+            }
+        }
+
+        // If we consumed all alphanumeric chars and still haven't reached clamped_raw_pos,
+        // place cursor at the end of the formatted string.
+        formatted.len()
+    }
+
+    fn formatted_to_raw(&self, raw: &str, formatted: &str, formatted_pos: usize) -> usize {
+        let clamped_fmt_pos = formatted_pos.min(formatted.len());
+
+        // Count alphanumerics in formatted up to formatted_pos.
+        let mut seen_user_chars = 0usize;
+        for (idx, ch) in formatted.char_indices() {
+            if idx >= clamped_fmt_pos {
+                break;
+            }
+            if ch.is_alphanumeric() {
+                seen_user_chars += 1;
+            }
+        }
+
+        // Map to raw position by clamping to raw char count
+        let raw_len = raw.chars().count();
+        seen_user_chars.min(raw_len)
+    }
+}
+
+/// Result of invoking a custom formatter on the raw input.
+///
+/// Success variants carry the formatted string and a position mapper to translate
+/// between raw and formatted cursor positions. If you don't provide a custom mapper,
+/// the library will fall back to DefaultPositionMapper.
+pub enum FormattingResult {
+    /// Successfully produced a formatted display value and a position mapper.
+    Success {
+        formatted: String,
+        /// Mapper to convert cursor positions between raw and formatted representations.
+        mapper: Arc<dyn PositionMapper>,
+    },
+    /// Successfully produced a formatted value, but with a non-fatal warning message
+    /// that can be shown in the UI (e.g., "incomplete value").
+    Warning {
+        formatted: String,
+        message: String,
+        mapper: Arc<dyn PositionMapper>,
+    },
+    /// Failed to produce a formatted display. The library will typically fall back to raw.
+    Error {
+        message: String,
+    },
+}
+
+impl FormattingResult {
+    /// Convenience to create a success result using the default mapper.
+    pub fn success(formatted: impl Into<String>) -> Self {
+        FormattingResult::Success {
+            formatted: formatted.into(),
+            mapper: Arc::new(DefaultPositionMapper::default()),
+        }
+    }
+
+    /// Convenience to create a warning result using the default mapper.
+    pub fn warning(formatted: impl Into<String>, message: impl Into<String>) -> Self {
+        FormattingResult::Warning {
+            formatted: formatted.into(),
+            message: message.into(),
+            mapper: Arc::new(DefaultPositionMapper::default()),
+        }
+    }
+
+    /// Convenience to create a success result with a custom mapper.
+    pub fn success_with_mapper(
+        formatted: impl Into<String>,
+        mapper: Arc<dyn PositionMapper>,
+    ) -> Self {
+        FormattingResult::Success {
+            formatted: formatted.into(),
+            mapper,
+        }
+    }
+
+    /// Convenience to create a warning result with a custom mapper.
+    pub fn warning_with_mapper(
+        formatted: impl Into<String>,
+        message: impl Into<String>,
+        mapper: Arc<dyn PositionMapper>,
+    ) -> Self {
+        FormattingResult::Warning {
+            formatted: formatted.into(),
+            message: message.into(),
+            mapper,
+        }
+    }
+
+    /// Convenience to create an error result.
+    pub fn error(message: impl Into<String>) -> Self {
+        FormattingResult::Error {
+            message: message.into(),
+        }
+    }
+}
+
+/// A user-implemented formatter that turns raw input into a formatted display string,
+/// optionally providing a custom cursor position mapper.
+///
+/// Notes:
+/// - The library will keep raw input authoritative for editing and validation.
+/// - The formatted value is only used for display.
+/// - If formatting fails, return Error; the library will show the raw value.
+/// - For common grouping (spaces/dashes), you can return Success/Warning and rely
+///   on DefaultPositionMapper, or provide your own mapper for advanced cases
+///   (reordering, compression, locale-specific rules, etc.).
+pub trait CustomFormatter: Send + Sync {
+    fn format(&self, raw: &str) -> FormattingResult;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    struct GroupEvery3;
+    impl CustomFormatter for GroupEvery3 {
+        fn format(&self, raw: &str) -> FormattingResult {
+            let mut out = String::new();
+            for (i, ch) in raw.chars().enumerate() {
+                if i > 0 && i % 3 == 0 {
+                    out.push(' ');
+                }
+                out.push(ch);
+            }
+            FormattingResult::success(out)
+        }
+    }
+
+    #[test]
+    fn default_mapper_roundtrip_basic() {
+        let mapper = DefaultPositionMapper::default();
+        let raw = "01001";
+        let formatted = "010 01";
+
+        // raw_to_formatted monotonicity and bounds
+        for rp in 0..=raw.chars().count() {
+            let fp = mapper.raw_to_formatted(raw, formatted, rp);
+            assert!(fp <= formatted.len());
+        }
+
+        // formatted_to_raw bounds
+        for fp in 0..=formatted.len() {
+            let rp = mapper.formatted_to_raw(raw, formatted, fp);
+            assert!(rp <= raw.chars().count());
+        }
+    }
+
+    #[test]
+    fn formatter_groups_every_3() {
+        let f = GroupEvery3;
+        match f.format("1234567") {
+            FormattingResult::Success { formatted, .. } => {
+                assert_eq!(formatted, "123 456 7");
+            }
+            _ => panic!("expected success"),
+        }
+    }
+}

canvas/src/validation/mod.rs

@@ -6,6 +6,7 @@ pub mod limits;
 pub mod state;
 pub mod patterns;
 pub mod mask;  // Simple display mask instead of complex reserved chars
+pub mod formatting; // Custom formatter and position mapping (feature 4)
 
 // Re-export main types
 pub use config::{ValidationConfig, ValidationResult, ValidationConfigBuilder};
@@ -13,6 +14,17 @@ pub use limits::{CharacterLimits, LimitCheckResult};
 pub use state::{ValidationState, ValidationSummary};
 pub use patterns::{PatternFilters, PositionFilter, PositionRange, CharacterFilter};
 pub use mask::DisplayMask;  // Simple mask instead of ReservedCharacters
+pub use formatting::{CustomFormatter, FormattingResult, PositionMapper, DefaultPositionMapper};
+
+/// External validation UI state (Feature 5)
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ExternalValidationState {
+    NotValidated,
+    Validating,
+    Valid(Option<String>),
+    Invalid { message: String, suggestion: Option<String> },
+    Warning { message: String },
+}
 
 /// Validation error types
 #[derive(Debug, Clone, thiserror::Error)]

canvas/src/validation/state.rs

@@ -1,7 +1,7 @@
 // src/validation/state.rs
 //! Validation state management
 
-use crate::validation::{ValidationConfig, ValidationResult};
+use crate::validation::{ValidationConfig, ValidationResult, ExternalValidationState};
 use std::collections::HashMap;
 
 /// Validation state for all fields in a form
@@ -18,6 +18,9 @@ pub struct ValidationState {
     
     /// Global validation enabled/disabled
     enabled: bool,
+
+    /// External validation results per field (Feature 5)
+    external_results: HashMap<usize, ExternalValidationState>,
 }
 
 impl ValidationState {
@@ -28,6 +31,7 @@ impl ValidationState {
             field_results: HashMap::new(),
             validated_fields: std::collections::HashSet::new(),
             enabled: true,
+            external_results: HashMap::new(),
         }
     }
     
@@ -38,6 +42,7 @@ impl ValidationState {
             // Clear all validation results when disabled
             self.field_results.clear();
             self.validated_fields.clear();
+            self.external_results.clear(); // Also clear external results
         }
     }
     
@@ -48,12 +53,13 @@ impl ValidationState {
     
     /// Set validation configuration for a field
     pub fn set_field_config(&mut self, field_index: usize, config: ValidationConfig) {
-        if config.has_validation() {
+        if config.has_validation() || config.external_validation_enabled {
             self.field_configs.insert(field_index, config);
         } else {
             self.field_configs.remove(&field_index);
             self.field_results.remove(&field_index);
             self.validated_fields.remove(&field_index);
+            self.external_results.remove(&field_index);
         }
     }
     
@@ -67,6 +73,30 @@ impl ValidationState {
         self.field_configs.remove(&field_index);
         self.field_results.remove(&field_index);
         self.validated_fields.remove(&field_index);
+        self.external_results.remove(&field_index);
+    }
+    
+    /// Set external validation state for a field (Feature 5)
+    pub fn set_external_validation(&mut self, field_index: usize, state: ExternalValidationState) {
+        self.external_results.insert(field_index, state);
+    }
+    
+    /// Get current external validation state for a field
+    pub fn get_external_validation(&self, field_index: usize) -> ExternalValidationState {
+        self.external_results
+            .get(&field_index)
+            .cloned()
+            .unwrap_or(ExternalValidationState::NotValidated)
+    }
+    
+    /// Clear external validation state for a field
+    pub fn clear_external_validation(&mut self, field_index: usize) {
+        self.external_results.remove(&field_index);
+    }
+    
+    /// Clear all external validation states
+    pub fn clear_all_external_validation(&mut self) {
+        self.external_results.clear();
     }
     
     /// Validate character insertion for a field
@@ -122,6 +152,18 @@ impl ValidationState {
         self.field_results.get(&field_index)
     }
     
+    /// Get formatted display for a field if a custom formatter is configured.
+    /// Returns (formatted_text, position_mapper, optional_warning_message).
+    #[cfg(feature = "validation")]
+    pub fn formatted_for(
+        &self,
+        field_index: usize,
+        raw: &str,
+    ) -> Option<(String, std::sync::Arc<dyn crate::validation::PositionMapper>, Option<String>)> {
+        let config = self.field_configs.get(&field_index)?;
+        config.run_custom_formatter(raw)
+    }
+    
     /// Check if a field has been validated
     pub fn is_field_validated(&self, field_index: usize) -> bool {
         self.validated_fields.contains(&field_index)

canvas/view_docs.sh

@@ -27,7 +27,7 @@ show_module() {
 
 # Main modules
 show_module "canvas" "CANVAS SYSTEM"
-show_module "autocomplete" "AUTOCOMPLETE SYSTEM" 
+show_module "suggestions" "SUGGESTIONS SYSTEM" 
 show_module "config" "CONFIGURATION SYSTEM"
 
 # Show lib.rs and other root files
@@ -45,7 +45,7 @@ fi
 echo -e "\n\033[1;36m=========================================="
 echo "To view specific module documentation:"
 echo "  ./view_canvas_docs.sh canvas"
-echo "  ./view_canvas_docs.sh autocomplete" 
+echo "  ./view_canvas_docs.sh suggestions" 
 echo "  ./view_canvas_docs.sh config"
 echo "==========================================\033[0m"