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+# PNG Metadata Editor - Technical Documentation
+
+## Table of Contents
+1. [Overview](#overview)
+2. [Features](#features)
+3. [Code Structure](#code-structure)
+4. [Key Components](#key-components)
+5. [Data Flow](#data-flow)
+6. [API Reference](#api-reference)
+7. [Usage Examples](#usage-examples)
+8. [Troubleshooting](#troubleshooting)
+
+## Overview
+
+PNG Metadata Editor is a graphical application built with Python and Tkinter that allows users to view, edit, add, and delete metadata in PNG files. The application leverages the Pillow library for PNG manipulation.
+
+## Features
+
+### Core Functionality
+- **Metadata Viewing**: Display all text chunks (tEXt, zTXt, iTXt) in PNG files
+- **Metadata Editing**: Add, modify, and delete metadata fields
+- **JSON Support**: Pretty-print JSON-formatted values
+- **Clipboard Integration**: Copy metadata values to clipboard
+
+### UI Features
+- Split-pane view with tree and detail panels
+- Status bar with temporary messages
+- Unsaved changes indicator
+- Responsive dialogs for adding/editing fields
+
+## Code Structure
+
+```
+png-meta-editor.py
+├── PNGMetadataEditor (Main Class)
+│   ├── __init__() - Initialization
+│   ├── setup_ui() - UI Construction
+│   ├── open_file() - File Operations
+│   ├── save_changes() - Save Functionality
+│   └── Various helper methods
+└── Supporting Functions
+    ├── format_value_for_display()
+    ├── truncate_value()
+    └── mark_as_modified()
+```
+
+## Key Components
+
+### Main Application Class
+```python
+class PNGMetadataEditor:
+    def __init__(self, root):
+        # Initialize application state
+        self.current_file = None
+        self.metadata_dict = {}
+        self.has_unsaved_changes = False
+```
+
+### UI Components
+- **Treeview**: Displays metadata keys with truncated values
+- **Detail Text**: Shows full value of selected metadata
+- **Status Bar**: Provides feedback messages
+- **Dialogs**: Modal windows for adding/editing fields
+
+### Data Handling
+```python
+def open_file(self):
+    """Load PNG file and extract metadata"""
+    img = Image.open(filepath)
+    self.metadata_dict = dict(img.text)  # Extract all text chunks
+```
+
+## Data Flow
+
+1. **File Opening**:
+   - User selects PNG file → `open_file()` called
+   - PIL extracts text chunks → stored in `metadata_dict`
+   - UI refreshed with new data
+
+2. **Editing Process**:
+   - User selects field → `on_selection_change()` updates detail view
+   - Edit initiated → `edit_entry()` opens dialog
+   - Changes saved → `mark_as_modified()` updates state
+
+3. **Saving**:
+   - User clicks Save → `save_changes()` called
+   - New PngInfo object created with updated metadata
+   - File saved with `img.save()` using new metadata
+
+## API Reference
+
+### Public Methods
+| Method | Description |
+|--------|-------------|
+| `open_file()` | Loads PNG file and extracts metadata |
+| `save_changes()` | Saves current metadata to file |
+| `add_field()` | Opens dialog to add new metadata field |
+| `edit_entry()` | Opens dialog to edit selected field |
+| `delete_field()` | Removes selected metadata field |
+
+### Helper Methods
+```python
+def format_value_for_display(self, value):
+    """Try to parse as JSON for pretty printing"""
+    try:
+        return json.dumps(json.loads(value), indent=2)
+    except:
+        return str(value)
+
+def truncate_value(self, value, max_length=80):
+    """Shorten long values for tree display"""
+    return str(value)[:max_length] + "..." if len(str(value)) > max_length else str(value)
+```
+
+## Usage Examples
+
+### Basic Workflow
+```python
+# Initialize application
+root = tk.Tk()
+app = PNGMetadataEditor(root)
+
+# Open a file (simulated)
+app.current_file = "example.png"
+img = Image.open("example.png")
+app.metadata_dict = dict(img.text)
+app.refresh_tree()
+
+# Edit a field
+app.edit_entry()  # Would normally be triggered by UI event
+
+# Save changes
+app.save_changes()
+```
+
+### Programmatic Access
+```python
+# Get all metadata as dictionary
+metadata = app.metadata_dict
+
+# Add new field programmatically
+app.metadata_dict["NewField"] = "Value"
+app.mark_as_modified()
+app.refresh_tree()
+
+# Check for unsaved changes
+if app.has_unsaved_changes:
+    print("There are unsaved changes!")
+```
+
+## Troubleshooting
+
+### Common Issues
+1. **File Not Opening**:
+   - Ensure file is a valid PNG
+   - Check file permissions
+
+2. **Metadata Not Displaying**:
+   - Verify PNG contains text chunks
+   - Check for special characters in keys/values
+
+3. **Save Failures**:
+   - Ensure file isn't read-only
+   - Verify write permissions to directory
+
+### Debugging Tips
+- Check status bar for error messages
+- Review console output for exceptions
+- Verify metadata_dict contents in debugger
+
+## Development Notes
+
+### Design Decisions
+1. **State Management**: Uses `has_unsaved_changes` flag to track modifications
+2. **UI Separation**: Treeview and detail view maintain separate data representations
+3. **Error Handling**: Graceful degradation with user-friendly messages
+
+### Future Improvements
+- Batch processing for multiple files
+- Metadata validation rules
+- Export/import to JSON
+- Advanced search functionality
+
+## Contributing
+
+When contributing to this project:
+1. Fork the repository
+2. Create a feature branch
+3. Submit a pull request with tests
+
+For major changes, please open an issue first to discuss what you would like to change.