# Accessibility

MatPlotLibNet v0.8.8 adds first-class accessibility support across four areas: SVG semantic structure, keyboard navigation, color-blind safe palette, and high-contrast theme.

---

## SVG Semantics

Every SVG produced by MatPlotLibNet carries:

| Attribute / Element | Value | Purpose |
|---|---|---|
| `role="img"` | on `<svg>` | Marks the SVG as an image for assistive tech |
| `<title id="chart-title">` | alt text → figure title → empty | Screen-reader label |
| `<desc id="chart-desc">` | `Figure.Description` (optional) | Longer description |
| `aria-labelledby="chart-title"` | on `<svg>` | Links to `<title>` |
| `aria-describedby="chart-desc"` | on `<svg>` when description set | Links to `<desc>` |
| `aria-label="Chart legend"` | on legend group | Identifies legend section |
| `aria-label="Color bar"` | on color bar group | Identifies color bar |
| `aria-label="{series label}"` | on labeled series group | Names each data series |

### Setting Alt Text

```csharp
Plt.Create()
    .WithAltText("Monthly revenue Q1 2025")
    .WithDescription("Line chart showing revenue growth from Jan to Mar 2025, peaking at $3.2M in March.")
    .Plot(months, revenue)
    .Save("revenue.svg");
```

`WithAltText` maps to the SVG `<title>` element. If omitted, `WithTitle` is used as the fallback. `WithDescription` maps to `<desc>` and is optional.

---

## Keyboard Navigation

All five interactive SVG features are keyboard-accessible:

### Legend Toggle

- Each legend entry receives `role="button"`, `tabindex="0"`, and `aria-pressed="false"`
- Press **Enter** or **Space** to toggle series visibility
- `aria-pressed` updates to reflect current state

### Series Highlight

- Each series group receives `tabindex="0"`
- **Focus** highlights the series (dims siblings); **Blur** restores all

### Zoom / Pan

- The SVG receives `tabindex="0"` and `aria-roledescription="interactive chart"`
- **`+`** or **`=`**: zoom in
- **`-`**: zoom out
- **Arrow keys** (←→↑↓): pan
- **`Home`**: reset to original view

### Selection

- **Escape**: cancel an active shift-drag selection rectangle

### Tooltips

- Tooltip div carries `role="tooltip"` and `aria-live="polite"`
- **Focus** on a `<title>`-parent element triggers the tooltip; **Blur** hides it

---

## Color-Blind Safe Palette

`Theme.ColorBlindSafe` uses the [Okabe-Ito](https://jfly.uni-koeln.de/color/) 8-color palette, which is distinguishable under all three common forms of color vision deficiency.

```csharp
Plt.Create()
    .WithTheme(Theme.ColorBlindSafe)
    .Plot(x, y, s => s.Label = "Revenue")
    .Plot(x, y2, s => s.Label = "Cost")
    .Save("colorblind.svg");
```

The palette is also available as a colormap:

```csharp
// Named "okabe_ito" / "okabe_ito_r" in the registry
var map = ColorMaps.Get("okabe_ito");
```

Colors (in cycle order):

| # | Hex | Name |
|---|---|---|
| 1 | `#E69F00` | Orange |
| 2 | `#56B4E9` | Sky blue |
| 3 | `#009E73` | Bluish green |
| 4 | `#F0E442` | Yellow |
| 5 | `#0072B2` | Blue |
| 6 | `#D55E00` | Vermillion |
| 7 | `#CC79A7` | Reddish purple |
| 8 | `#000000` | Black |

---

## High-Contrast Theme

`Theme.HighContrast` targets WCAG AAA (7:1 contrast ratio). Pure white background and pure black text yield a 21:1 contrast ratio. The default font is bold at 13pt; the grid is 1.5px dark.

```csharp
Plt.Create()
    .WithTheme(Theme.HighContrast)
    .Plot(x, y)
    .Save("high-contrast.svg");
```

---

## Serialization

`Figure.AltText` and `Figure.Description` are included in the JSON round-trip:

```csharp
var figure = Plt.Create()
    .WithAltText("Sales chart")
    .WithDescription("Monthly sales data for 2025")
    .Plot(x, y)
    .Build();

string json = ChartServices.Serializer.ToJson(figure);   // includes altText / description
Figure restored = ChartServices.Serializer.FromJson(json); // restores both properties
```