# Panel Component

## Introduction

The Panel component provides a flexible three-zone layout with optional collapsible side panels. It's designed to
organize content into left panel, main area, and right panel sections, with smooth toggle animations and resizable
panels.

**Key features:**

- Three customizable zones (left panel, main content, right panel)
- Configurable panel titles with sticky headers
- Toggle visibility with hide/show icons
- Resizable panels with drag handles
- Smooth CSS animations for show/hide transitions
- Automatic state persistence per session
- Configurable panel presence (enable/disable left or right)
- Session-based width and visibility state

**Common use cases:**

- Code editor with file explorer and properties panel
- Data visualization with filters sidebar and details panel
- Admin interface with navigation menu and tools panel
- Documentation viewer with table of contents and metadata
- Dashboard with configuration panel and information sidebar

## Quick Start

Here's a minimal example showing a three-panel layout for a code editor:

```python
from fasthtml.common import *
from myfasthtml.controls.Panel import Panel

# Create the panel instance
panel = Panel(parent=root_instance)

# Set content for each zone
panel.set_left(
  Div(
    H3("Files"),
    Ul(
      Li("app.py"),
      Li("config.py"),
      Li("utils.py")
    )
  )
)

panel.set_main(
  Div(
    H2("Editor"),
    Textarea("# Write your code here", rows=20, cls="w-full font-mono")
  )
)

panel.set_right(
  Div(
    H3("Properties"),
    Div("Language: Python"),
    Div("Lines: 120"),
    Div("Size: 3.2 KB")
  )
)

# Render the panel
return panel
```

This creates a complete panel layout with:

- A left panel displaying a file list with a hide icon (−) at the top right
- A main content area with a code editor
- A right panel showing file properties with a hide icon (−) at the top right
- Show icons (⋯) that appear in the main area when panels are hidden
- Drag handles between panels for manual resizing
- Automatic state persistence (visibility and width)

**Note:** Users can hide panels by clicking the hide icon (−) inside each panel. When hidden, a show icon (⋯) appears in
the main area (left side for left panel, right side for right panel). Panels can be resized by dragging the handles, and
all state is automatically saved in the session.

## Basic Usage

### Visual Structure

The Panel component consists of three zones with optional side panels:

```
┌────────────────────────────────────────────────────────────┐
│                                                            │
│  ┌──────────┐ │ ┌──────────────────────┐ │ ┌──────────┐    │
│  │          │ │ │                      │ │ │          │    │
│  │   Left   │ ║ │                      │ ║ │  Right   │    │
│  │  Panel   │ │ │    Main Content      │ │ │  Panel   │    │
│  │          │ │ │                      │ │ │          │    │
│  │     [−]  │ │ │  [⋯]         [⋯]    │ │ │  [−]     │    │
│  └──────────┘ │ └──────────────────────┘ │ └──────────┘    │
│               ║                          ║                 │
│            Resizer                    Resizer              │
└────────────────────────────────────────────────────────────┘
```

**Component details:**

| Element       | Description                                   |
|---------------|-----------------------------------------------|
| Left panel    | Optional collapsible panel (default: visible) |
| Main content  | Always-visible central content area           |
| Right panel   | Optional collapsible panel (default: visible) |
| Hide icon (−) | Inside each panel header, right side          |
| Show icon (⋯) | In main area when panel is hidden             |
| Resizer (║)   | Drag handle to resize panels manually         |

**Panel with title (default):**

When `show_left_title` or `show_right_title` is `True` (default), panels display a sticky header with title and hide icon:

```
┌─────────────────────────────┐
│ Title               [−]     │  ← Header (sticky, always visible)
├─────────────────────────────┤
│                             │
│    Scrollable Content       │  ← Content area (scrolls independently)
│                             │
└─────────────────────────────┘
```

**Panel without title:**

When `show_left_title` or `show_right_title` is `False`, panels use the legacy layout:

```
┌─────────────────────────────┐
│                        [−]  │  ← Hide icon at top-right (absolute)
│                             │
│         Content             │
│                             │
└─────────────────────────────┘
```

### Creating a Panel

The Panel is a `MultipleInstance`, meaning you can create multiple independent panels in your application. Create it by
providing a parent instance:

```python
panel = Panel(parent=root_instance)

# Or with a custom ID
panel = Panel(parent=root_instance, _id="my-panel")

# Or with custom configuration
from myfasthtml.controls.Panel import PanelConf

conf = PanelConf(left=True, right=False)  # Only left panel enabled
panel = Panel(parent=root_instance, conf=conf)
```

### Content Zones

The Panel provides three content zones:

```
┌─────────────────────────────────────────────────────┐
│  Left Panel  │  Main Content  │  Right Panel        │
│  (optional)  │   (required)   │  (optional)         │
└─────────────────────────────────────────────────────┘
```

**Zone details:**

| Zone    | Typical Use                                           | Required |
|---------|-------------------------------------------------------|----------|
| `left`  | Navigation, file explorer, filters, table of contents | No       |
| `main`  | Primary content, editor, visualization, results       | Yes      |
| `right` | Properties, tools, metadata, debug info, settings     | No       |

### Setting Content

Use the `set_*()` methods to add content to each zone:

```python
# Main content (always visible)
panel.set_main(
  Div(
    H1("Dashboard"),
    P("This is the main content area")
  )
)

# Left panel (optional)
panel.set_left(
  Div(
    H3("Navigation"),
    Ul(
      Li("Home"),
      Li("Settings"),
      Li("About")
    )
  )
)

# Right panel (optional)
panel.set_right(
  Div(
    H3("Tools"),
    Button("Export"),
    Button("Refresh")
  )
)
```

**Method chaining:**

The `set_main()` method returns `self`, enabling method chaining:

```python
panel = Panel(parent=root_instance)
  .set_main(Div("Main content"))
  .set_left(Div("Left content"))
```

### Panel Configuration

By default, both left and right panels are enabled with titles. You can customize this with `PanelConf`:

```python
from myfasthtml.controls.Panel import PanelConf

# Only left panel enabled
conf = PanelConf(left=True, right=False)
panel = Panel(parent=root_instance, conf=conf)

# Only right panel enabled
conf = PanelConf(left=False, right=True)
panel = Panel(parent=root_instance, conf=conf)

# Both panels enabled (default)
conf = PanelConf(left=True, right=True)
panel = Panel(parent=root_instance, conf=conf)

# No side panels (main content only)
conf = PanelConf(left=False, right=False)
panel = Panel(parent=root_instance, conf=conf)
```

**Customizing panel titles:**

```python
# Custom titles for panels
conf = PanelConf(
    left=True,
    right=True,
    left_title="Explorer",      # Custom title for left panel
    right_title="Properties"    # Custom title for right panel
)
panel = Panel(parent=root_instance, conf=conf)
```

**Disabling panel titles:**

When titles are disabled, panels use the legacy layout without a sticky header:

```python
# Disable titles (legacy layout)
conf = PanelConf(
    left=True,
    right=True,
    show_left_title=False,
    show_right_title=False
)
panel = Panel(parent=root_instance, conf=conf)
```

**Disabling show icons:**

You can hide the show icons (⋯) that appear when panels are hidden. This means users can only show panels programmatically:

```python
# Disable show icons (programmatic control only)
conf = PanelConf(
    left=True,
    right=True,
    show_display_left=False,   # No show icon for left panel
    show_display_right=False   # No show icon for right panel
)
panel = Panel(parent=root_instance, conf=conf)
```

**Note:** When a panel is disabled in configuration, it won't render at all. When a panel is hidden (via toggle), it
renders but with zero width and overflow hidden.

## Advanced Features

### Toggling Panel Visibility

Each visible panel includes a hide icon (−) in its top-right corner. When hidden, a show icon (⋯) appears in the main
area:

**User interaction:**

- **Hide panel**: Click the − icon inside the panel
- **Show panel**: Click the ⋯ icon in the main area

**Icon positions:**

- Hide icons (−): Always at top-right of each panel
- Show icon for left panel (⋯): Top-left of main area
- Show icon for right panel (⋯): Top-right of main area

**Visual states:**

```
Panel Visible:
┌──────────┐
│ Content  │
│     [−]  │  ← Hide icon visible
└──────────┘

Panel Hidden:
┌──────────────────┐
│ [⋯]       Main   │  ← Show icon visible in main
└──────────────────┘
```

**Animation:**

When toggling visibility:

- **Hiding**: Panel width animates to 0px over 0.3s
- **Showing**: Panel width animates to its saved width over 0.3s
- Content remains in DOM (state preserved)
- Smooth CSS transition with ease timing

**Note:** The animation only works when showing (panel appearing). When hiding, the transition currently doesn't apply
due to HTMX swap timing. This is a known limitation.

### Resizable Panels

Both left and right panels can be resized by users via drag handles:

- **Drag handle location**:
    - Left panel: Right edge (vertical bar)
    - Right panel: Left edge (vertical bar)
- **Width constraints**: 150px (minimum) to 500px (maximum)
- **Persistence**: Resized width is automatically saved in session state
- **No transition during resize**: CSS transitions are disabled during manual dragging for smooth performance

**How to resize:**

1. Hover over the panel edge (cursor changes to resize cursor)
2. Click and drag left/right
3. Release to set the new width
4. Width is saved automatically and persists in the session

**Initial widths:**

- Left panel: 250px
- Right panel: 250px

These defaults can be customized via state after creation if needed.

### State Persistence

The Panel automatically persists its state within the user's session:

| State Property  | Description                    | Default |
|-----------------|--------------------------------|---------|
| `left_visible`  | Whether left panel is visible  | `True`  |
| `right_visible` | Whether right panel is visible | `True`  |
| `left_width`    | Left panel width in pixels     | `250`   |
| `right_width`   | Right panel width in pixels    | `250`   |

State changes (toggle visibility, resize width) are automatically saved and restored within the session.

**Accessing state:**

```python
# Check current state
is_left_visible = panel._state.left_visible
left_panel_width = panel._state.left_width

# Programmatically update state (not recommended - use commands instead)
panel._state.left_visible = False  # Better to use toggle_side command
```

### Programmatic Control

You can control panels programmatically using commands:

```python
# Toggle panel visibility
toggle_left = panel.commands.set_side_visible("left", visible=False)  # Hide left
toggle_right = panel.commands.set_side_visible("right", visible=True)  # Show right

# Update panel width
update_left_width = panel.commands.update_side_width("left")
update_right_width = panel.commands.update_side_width("right")
```

These commands are typically used with buttons or other interactive elements:

```python
from myfasthtml.controls.helpers import mk

# Add buttons to toggle panels
hide_left_btn = mk.button("Hide Left", command=panel.commands.set_side_visible("left", False))
show_left_btn = mk.button("Show Left", command=panel.commands.set_side_visible("left", True))

# Add to your layout
panel.set_main(
  Div(
    hide_left_btn,
    show_left_btn,
    H1("Main Content")
  )
)
```

**Command details:**

- `toggle_side(side, visible)`: Sets panel visibility explicitly
    - `side`: `"left"` or `"right"`
    - `visible`: `True` (show) or `False` (hide)
    - Returns: tuple of (panel_element, show_icon_element) for HTMX swap

- `update_side_width(side)`: Updates panel width from HTMX request
    - `side`: `"left"` or `"right"`
    - Width value comes from JavaScript resize handler
    - Returns: updated panel element for HTMX swap

### CSS Customization

The Panel uses CSS classes that you can customize:

| Class                      | Element                                    |
|----------------------------|--------------------------------------------|
| `mf-panel`                 | Root panel container                       |
| `mf-panel-left`            | Left panel container                       |
| `mf-panel-right`           | Right panel container                      |
| `mf-panel-main`            | Main content area                          |
| `mf-panel-with-title`      | Panel using title layout (no padding-top)  |
| `mf-panel-body`            | Grid container for header + content        |
| `mf-panel-header`          | Sticky header with title and hide icon     |
| `mf-panel-content`         | Scrollable content area                    |
| `mf-panel-hide-icon`       | Hide icon (−) inside panels                |
| `mf-panel-show-icon`       | Show icon (⋯) in main area                 |
| `mf-panel-show-icon-left`  | Show icon for left panel                   |
| `mf-panel-show-icon-right` | Show icon for right panel                  |
| `mf-resizer`               | Resize handle base class                   |
| `mf-resizer-left`          | Left panel resize handle                   |
| `mf-resizer-right`         | Right panel resize handle                  |
| `mf-hidden`                | Applied to hidden panels                   |
| `no-transition`            | Disables transition during manual resize   |

**Example customization:**

```css
/* Change panel background color */
.mf-panel-left,
.mf-panel-right {
    background-color: #f9fafb;
}

/* Customize hide icon appearance */
.mf-panel-hide-icon:hover {
    background-color: rgba(0, 0, 0, 0.1);
    color: #ef4444;
}

/* Change transition timing */
.mf-panel-left,
.mf-panel-right {
    transition: width 0.5s ease-in-out; /* Slower animation */
}

/* Style resizer handles */
.mf-resizer {
    background-color: #e5e7eb;
}

.mf-resizer:hover {
    background-color: #3b82f6;
}
```

## Examples

### Example 1: Code Editor Layout

A typical code editor with file explorer, editor, and properties panel:

```python
from fasthtml.common import *
from myfasthtml.controls.Panel import Panel

# Create panel
panel = Panel(parent=root_instance)

# Left panel: File Explorer
panel.set_left(
  Div(
    H3("Explorer", cls="font-bold mb-2"),
    Div(
      Div("📁 src", cls="font-mono cursor-pointer"),
      Div("  📄 app.py", cls="font-mono ml-4 cursor-pointer"),
      Div("  📄 config.py", cls="font-mono ml-4 cursor-pointer"),
      Div("📁 tests", cls="font-mono cursor-pointer"),
      Div("  📄 test_app.py", cls="font-mono ml-4 cursor-pointer"),
      cls="space-y-1"
    ),
    cls="p-4"
  )
)

# Main: Code Editor
panel.set_main(
  Div(
    Div(
      Span("app.py", cls="font-bold"),
      Span("Python", cls="text-sm opacity-60 ml-2"),
      cls="border-b pb-2 mb-2"
    ),
    Textarea(
      """def main():
print("Hello, World!")

if __name__ == "__main__":
main()""",
      rows=20,
      cls="w-full font-mono text-sm p-2 border rounded"
    ),
    cls="p-4"
  )
)

# Right panel: Properties and Tools
panel.set_right(
  Div(
    H3("Properties", cls="font-bold mb-2"),
    Div("Language: Python", cls="text-sm mb-1"),
    Div("Lines: 5", cls="text-sm mb-1"),
    Div("Size: 87 bytes", cls="text-sm mb-4"),
    
    H3("Tools", cls="font-bold mb-2 mt-4"),
    Button("Run", cls="btn btn-sm btn-primary w-full mb-2"),
    Button("Debug", cls="btn btn-sm w-full mb-2"),
    Button("Format", cls="btn btn-sm w-full"),
    cls="p-4"
  )
)

return panel
```

### Example 2: Dashboard with Filters

A data dashboard with filters sidebar and details panel:

```python
from fasthtml.common import *
from myfasthtml.controls.Panel import Panel

# Create panel
panel = Panel(parent=root_instance)

# Left panel: Filters
panel.set_left(
  Div(
    H3("Filters", cls="font-bold mb-3"),
    
    Div(
      Label("Date Range", cls="label"),
      Select(
        Option("Last 7 days"),
        Option("Last 30 days"),
        Option("Last 90 days"),
        cls="select select-bordered w-full"
      ),
      cls="mb-3"
    ),
    
    Div(
      Label("Category", cls="label"),
      Div(
        Label(Input(type="checkbox", cls="checkbox"), " Sales", cls="label cursor-pointer"),
        Label(Input(type="checkbox", cls="checkbox"), " Marketing", cls="label cursor-pointer"),
        Label(Input(type="checkbox", cls="checkbox"), " Support", cls="label cursor-pointer"),
        cls="space-y-2"
      ),
      cls="mb-3"
    ),
    
    Button("Apply Filters", cls="btn btn-primary w-full"),
    cls="p-4"
  )
)

# Main: Dashboard Charts
panel.set_main(
  Div(
    H1("Analytics Dashboard", cls="text-2xl font-bold mb-4"),
    
    Div(
      Div(
        Div("Total Revenue", cls="stat-title"),
        Div("$45,231", cls="stat-value"),
        Div("+12% from last month", cls="stat-desc"),
        cls="stat"
      ),
      Div(
        Div("Active Users", cls="stat-title"),
        Div("2,345", cls="stat-value"),
        Div("+8% from last month", cls="stat-desc"),
        cls="stat"
      ),
      cls="stats shadow mb-4"
    ),
    
    Div("[Chart placeholder - Revenue over time]", cls="border rounded p-8 text-center"),
    cls="p-4"
  )
)

# Right panel: Details and Insights
panel.set_right(
  Div(
    H3("Key Insights", cls="font-bold mb-3"),
    
    Div(
      Div("🎯 Top Performing", cls="font-bold mb-1"),
      Div("Product A: $12,450", cls="text-sm"),
      Div("Product B: $8,920", cls="text-sm mb-3")
    ),
    
    Div(
      Div("📊 Trending Up", cls="font-bold mb-1"),
      Div("Category: Electronics", cls="text-sm"),
      Div("+23% this week", cls="text-sm mb-3")
    ),
    
    Div(
      Div("⚠️ Needs Attention", cls="font-bold mb-1"),
      Div("Low stock: Item X", cls="text-sm"),
      Div("Response time: +15%", cls="text-sm")
    ),
    cls="p-4"
  )
)

return panel
```

### Example 3: Simple Layout (Main Content Only)

A minimal panel with no side panels, focusing only on main content:

```python
from fasthtml.common import *
from myfasthtml.controls.Panel import Panel, PanelConf

# Create panel with both side panels disabled
conf = PanelConf(left=False, right=False)
panel = Panel(parent=root_instance, conf=conf)

# Only main content
panel.set_main(
  Article(
    H1("Welcome to My Blog", cls="text-3xl font-bold mb-4"),
    P("This is a simple layout focusing entirely on the main content."),
    P("No side panels distract from the reading experience."),
    P("The content takes up the full width of the container."),
    cls="prose max-w-none p-8"
  )
)

return panel
```

### Example 4: Dynamic Panel Updates

Controlling panels programmatically based on user interaction:

```python
from fasthtml.common import *
from myfasthtml.controls.Panel import Panel
from myfasthtml.controls.helpers import mk
from myfasthtml.core.commands import Command

# Create panel
panel = Panel(parent=root_instance)

# Set up content
panel.set_left(
  Div(
    H3("Navigation"),
    Ul(
      Li("Dashboard"),
      Li("Reports"),
      Li("Settings")
    )
  )
)

panel.set_right(
  Div(
    H3("Debug Info"),
    Div("Session ID: abc123"),
    Div("User: Admin"),
    Div("Timestamp: 2024-01-15")
  )
)

# Create control buttons
toggle_left_btn = mk.button(
  "Toggle Left Panel",
  command=panel.commands.set_side_visible("left", False),
  cls="btn btn-sm"
)

toggle_right_btn = mk.button(
  "Toggle Right Panel",
  command=panel.commands.set_side_visible("right", False),
  cls="btn btn-sm"
)

show_all_btn = mk.button(
  "Show All Panels",
  command=Command(
    "show_all",
    "Show all panels",
    lambda: (
            panel.toggle_side("left", True),
            panel.toggle_side("right", True)
    )
  ),
  cls="btn btn-sm btn-primary"
)

# Main content with controls
panel.set_main(
  Div(
    H1("Panel Controls Demo", cls="text-2xl font-bold mb-4"),

    Div(
      toggle_left_btn,
      toggle_right_btn,
      show_all_btn,
      cls="space-x-2 mb-4"
    ),

    P("Use the buttons above to toggle panels programmatically."),
    P("You can also use the hide (−) and show (⋯) icons."),

    cls="p-4"
  )
)

return panel
```

---

## Developer Reference

This section contains technical details for developers working on the Panel component itself.

### Configuration

The Panel component uses `PanelConf` dataclass for configuration:

| Property             | Type    | Description                               | Default   |
|----------------------|---------|-------------------------------------------|-----------|
| `left`               | boolean | Enable/disable left panel                 | `False`   |
| `right`              | boolean | Enable/disable right panel                | `True`    |
| `left_title`         | string  | Title displayed in left panel header      | `"Left"`  |
| `right_title`        | string  | Title displayed in right panel header     | `"Right"` |
| `show_left_title`    | boolean | Show title header on left panel           | `True`    |
| `show_right_title`   | boolean | Show title header on right panel          | `True`    |
| `show_display_left`  | boolean | Show the "show" icon when left is hidden  | `True`    |
| `show_display_right` | boolean | Show the "show" icon when right is hidden | `True`    |

### State

The Panel component maintains the following state properties via `PanelState`:

| Name            | Type    | Description                        | Default |
|-----------------|---------|------------------------------------|---------|
| `left_visible`  | boolean | True if the left panel is visible  | `True`  |
| `right_visible` | boolean | True if the right panel is visible | `True`  |
| `left_width`    | integer | Width of the left panel in pixels  | `250`   |
| `right_width`   | integer | Width of the right panel in pixels | `250`   |

### Commands

Available commands for programmatic control:

| Name                         | Description                                                       |
|------------------------------|-------------------------------------------------------------------|
| `toggle_side(side, visible)` | Sets panel visibility (side: "left"/"right", visible: True/False) |
| `update_side_width(side)`    | Updates panel width from HTMX request (side: "left"/"right")      |

**Note:** The old `toggle_side(side)` command without the `visible` parameter is deprecated but still available in the
codebase.

### Public Methods

| Method               | Description                  | Returns |
|----------------------|------------------------------|---------|
| `set_main(content)`  | Sets the main content area   | `self`  |
| `set_left(content)`  | Sets the left panel content  | `Div`   |
| `set_right(content)` | Sets the right panel content | `Div`   |
| `render()`           | Renders the complete panel   | `Div`   |

### High Level Hierarchical Structure

**With title (default, `show_*_title=True`):**

```
Div(id="{id}", cls="mf-panel")
├── Div(id="{id}_pl", cls="mf-panel-left mf-panel-with-title [mf-hidden]")
│   ├── Div(cls="mf-panel-body")
│   │   ├── Div(cls="mf-panel-header")
│   │   │   ├── Div [Title text]
│   │   │   └── Div (hide icon)
│   │   └── Div(id="{id}_cl", cls="mf-panel-content")
│   │       └── [Left content - scrollable]
│   └── Div (resizer-left)
├── Div(cls="mf-panel-main")
│   ├── Div(id="{id}_show_left", cls="hidden|mf-panel-show-icon-left")
│   ├── Div(id="{id}_m", cls="mf-panel-main")
│   │   └── [Main content]
│   └── Div(id="{id}_show_right", cls="hidden|mf-panel-show-icon-right")
├── Div(id="{id}_pr", cls="mf-panel-right mf-panel-with-title [mf-hidden]")
│   ├── Div (resizer-right)
│   └── Div(cls="mf-panel-body")
│       ├── Div(cls="mf-panel-header")
│       │   ├── Div [Title text]
│       │   └── Div (hide icon)
│       └── Div(id="{id}_cr", cls="mf-panel-content")
│           └── [Right content - scrollable]
└── Script  # initResizer('{id}')
```

**Without title (legacy, `show_*_title=False`):**

```
Div(id="{id}", cls="mf-panel")
├── Div(id="{id}_pl", cls="mf-panel-left [mf-hidden]")
│   ├── Div (hide icon - absolute positioned)
│   ├── Div(id="{id}_cl")
│   │   └── [Left content]
│   └── Div (resizer-left)
├── Div(cls="mf-panel-main")
│   ├── Div(id="{id}_show_left", cls="hidden|mf-panel-show-icon-left")
│   ├── Div(id="{id}_m", cls="mf-panel-main")
│   │   └── [Main content]
│   └── Div(id="{id}_show_right", cls="hidden|mf-panel-show-icon-right")
├── Div(id="{id}_pr", cls="mf-panel-right [mf-hidden]")
│   ├── Div (resizer-right)
│   ├── Div (hide icon - absolute positioned)
│   └── Div(id="{id}_cr")
│       └── [Right content]
└── Script  # initResizer('{id}')
```

**Note:**

- With title: uses grid layout (`mf-panel-body`) with sticky header and scrollable content
- Without title: hide icon is absolutely positioned at top-right with padding-top on panel
- Left panel: body/content then resizer (resizer on right edge)
- Right panel: resizer then body/content (resizer on left edge)
- `[mf-hidden]` class is conditionally applied when panel is hidden
- `mf-panel-with-title` class removes default padding-top when using title layout

### Element IDs

| Name             | Description                         |
|------------------|-------------------------------------|
| `{id}`           | Root panel container                |
| `{id}_pl`        | Left panel container                |
| `{id}_pr`        | Right panel container               |
| `{id}_cl`        | Left panel content wrapper          |
| `{id}_cr`        | Right panel content wrapper         |
| `{id}_m`         | Main content wrapper                |
| `{id}_show_left` | Show icon for left panel (in main)  |
| `{id}_show_right`| Show icon for right panel (in main) |

**Note:** `{id}` is the Panel instance ID (auto-generated UUID or custom `_id`).

**ID Management:**

The Panel component uses the `PanelIds` helper class to manage element IDs consistently. Access IDs programmatically:

```python
panel = Panel(parent=root_instance)

# Access IDs via get_ids()
panel.get_ids().panel("left")   # Returns "{id}_pl"
panel.get_ids().panel("right")  # Returns "{id}_pr"
panel.get_ids().left            # Returns "{id}_cl"
panel.get_ids().right           # Returns "{id}_cr"
panel.get_ids().main            # Returns "{id}_m"
panel.get_ids().content("left") # Returns "{id}_cl"
```

### Internal Methods

These methods are used internally for rendering:

| Method                | Description                                       |
|-----------------------|---------------------------------------------------|
| `_mk_panel(side)`     | Renders a panel (left or right) with all elements |
| `_mk_show_icon(side)` | Renders the show icon for a panel                 |

**Method details:**

- `_mk_panel(side)`:
    - Checks if panel is enabled in config
    - Creates resizer with command and data attributes
    - Creates hide icon with toggle command
    - Applies `mf-hidden` class if panel is not visible
    - Returns None if panel is disabled

- `_mk_show_icon(side)`:
    - Checks if panel is enabled in config
    - Returns None if panel is disabled or visible
    - Applies `hidden` (Tailwind) class if panel is visible
    - Applies positioning class based on side

### JavaScript Integration

The Panel component uses JavaScript for manual resizing:

**initResizer(panelId):**

- Initializes drag-and-drop resize functionality
- Adds/removes `no-transition` class during drag
- Sends width updates to server via HTMX
- Constrains width between 150px and 500px

**File:** `src/myfasthtml/assets/core/myfasthtml.js`
