Markdown Accessibility Skill

Reusable knowledge module for the markdown-a11y-assistant, markdown-scanner, and markdown-fixer agents and the markdown-accessibility always-on instructions. Provides pattern libraries, severity scoring, fix templates, emoji translation maps, diagram description templates, and GitHub anchor generation rules for comprehensive markdown accessibility auditing across 9 domains.

Domains Covered

1. Descriptive Links (WCAG 2.4.4) - Ambiguous link text, bare URLs, repeated identical text
2. Image Alt Text (WCAG 1.1.1) - Missing, empty, filename-as-alt, generic placeholders
3. Heading Hierarchy (WCAG 1.3.1 / 2.4.6) - Skipped levels, multiple H1s, bold-as-heading
4. Table Accessibility (WCAG 1.3.1) - Missing descriptions, empty headers, layout tables
5. Emoji (WCAG 1.3.3 / Cognitive) - Remove-all, remove-decorative, translate, or leave-unchanged modes
6. Mermaid and ASCII Diagrams (WCAG 1.1.1 / 1.3.1) - Replace with accessible text + collapsible source
7. Em-Dash / En-Dash Normalization (Cognitive) - Normalize to - or leave unchanged
8. Anchor Link Validation (WCAG 2.4.4) - Validate #anchor links against actual headings
9. Plain Language and List Structure (Cognitive) - Emoji bullets, passive voice, sentence length

Severity Scoring

Scoring Formula

File Score = 100 - (sum of weighted findings)

Critical: -15 pts each
Serious:  - 7 pts each
Moderate: - 3 pts each
Minor:    - 1 pt each

Floor: 0

Score Grades

Emoji Handling Modes

The agent supports four modes configured during Phase 0:

Emoji Translation Map

When using translate mode, replace each emoji with the parenthesized English equivalent:

For emoji not in this table: flag as needs-human-review. Do not guess.

Emoji Detection Unicode Ranges

[\u{1F600}-\u{1F64F}]  - Emoticons
[\u{1F300}-\u{1F5FF}]  - Misc symbols and pictographs
[\u{1F680}-\u{1F6FF}]  - Transport and map symbols
[\u{1F700}-\u{1F77F}]  - Alchemical symbols
[\u{1F780}-\u{1F7FF}]  - Geometric shapes extended
[\u{1F900}-\u{1F9FF}]  - Supplemental symbols
[\u{1FA70}-\u{1FAFF}]  - Symbols and pictographs extended
[\u{2600}-\u{26FF}]    - Misc symbols
[\u{2700}-\u{27BF}]    - Dingbats
[\u{1F1E0}-\u{1F1FF}]  - Flags
[\u{FE00}-\u{FE0F}]    - Variation selectors

Emoji-as-bullet pattern: list item where the first non-whitespace character is an emoji.

Pattern Library: Mermaid and ASCII Diagrams

Mermaid Detection

Lines matching ```mermaid (with optional leading spaces/tabs).

Mermaid Description Templates

Auto-generate description for: graph, flowchart, pie, gantt, mindmap, timeline. Flag for human review: sequenceDiagram, classDiagram, erDiagram, stateDiagram (complex enough to need human verification).

Mermaid Replacement Template

[Generated or user-provided text description - this is the primary accessible content]

<details>
<summary>Diagram source (Mermaid)</summary>

```mermaid
[original diagram source - unchanged]
```text

</details>

ASCII Diagram Detection

ASCII art patterns: non-code-block lines (or unnamed code blocks) containing combinations of +, -, |, /, \, >, <, ^, v, * forming a visual structure. Minimum 3 lines with consistent column alignment.

ASCII Diagram Replacement Template

[Generated or user-provided text description - this is the primary accessible content]

<details>
<summary>ASCII diagram</summary>

[original ASCII art - unchanged]

</details>

Pattern Library: Ambiguous Link Detection

Match these patterns (case-insensitive, trim whitespace):

Exact-match violations

here, click here, read more, learn more, more, more info,
link, details, info, go, see more, continue, start, download,
view, open, submit, this, that

Starts-with violations

click here to ..., read more about ..., learn more about ...,
here to ..., see more ...

URL-as-text pattern

Any link where visible text matches https?:// or www\.

Repeated identical text

Multiple [X](url1) and [X](url2) with same X but different URLs on the same page.

Safe patterns (do not flag)

• Badge links: [![text](img)](url) at top of README
• Section self-references: [Installation](#installation) where text matches heading
• Footer resource lists using the resource/tool name as text

Pattern Library: GitHub Anchor Generation

GitHub converts headings to anchor IDs using these rules:

1. Lowercase entire string
2. Remove all characters except: letters (a-z), digits (0-9), spaces, hyphens
3. Replace spaces with hyphens
4. Remove leading and trailing hyphens

Examples

For headings containing emoji: GitHub strips the emoji character and generates an anchor from the remaining text. Anchors referencing emoji-containing headings are fragile and should be flagged.

Pattern Library: Emoji Detection

Unicode emoji ranges for regex detection:

[\u{1F600}-\u{1F64F}]  # Emoticons
[\u{1F300}-\u{1F5FF}]  # Misc symbols and pictographs
[\u{1F680}-\u{1F6FF}]  # Transport and map symbols
[\u{1F700}-\u{1F77F}]  # Alchemical symbols
[\u{1F780}-\u{1F7FF}]  # Geometric shapes extended
[\u{1F800}-\u{1F8FF}]  # Supplemental arrows-C
[\u{1F900}-\u{1F9FF}]  # Supplemental symbols and pictographs
[\u{1FA00}-\u{1FA6F}]  # Chess symbols
[\u{1FA70}-\u{1FAFF}]  # Symbols and pictographs extended-A
[\u{2600}-\u{26FF}]    # Misc symbols
[\u{2700}-\u{27BF}]    # Dingbats
[\u{FE00}-\u{FE0F}]    # Variation selectors
[\u{1F1E0}-\u{1F1FF}]  # Flags

Emoji-as-bullet pattern: List item where first non-whitespace character is an emoji.

Pattern Library: Em-Dash and En-Dash

Detection patterns:

—           Unicode em-dash (U+2014)
–           Unicode en-dash (U+2013)
---         Three hyphens in prose (not on its own line as HR)
--          Two hyphens in prose (used as em-dash substitute)

Safe to skip (do not modify):

• Line containing only --- (horizontal rule)
• Content inside ``` code fences
• Content inside backtick inline code
• YAML front matter block
• HTML comment blocks <!-- -->

Replacement: - (space + hyphen + space)

En-dash in numeric ranges: 2–4 hours -> 2 - 4 hours

Pattern Library: Mermaid Diagrams

Detection: Lines matching ```mermaid (with optional leading spaces/tabs)

Diagram types and description guidance:

Wrapping template:

[Generated or user-provided text description]

<details>
<summary>Diagram source (Mermaid)</summary>

```mermaid
[original diagram source]
```text

</details>

Fix Templates

Ambiguous link fix

# Before
For more information, see [here](https://example.com/guide).

# After
For more information, see the [installation guide](https://example.com/guide).

Emoji bullet fix

# Before
- 🚀 Deploy to production
- ✅ Run tests

# After
- Deploy to production
- Run tests

Emoji heading fix

# Before
## 🔧 Configuration

# After
## Configuration

Em-dash fix

# Before
The agent—when invoked—will scan all files.

# After
The agent - when invoked - will scan all files.

Table description fix

# Before
| Rule | Severity | Auto-fix |
|------|----------|----------|

# After
The following table lists rules with their severity level and whether they can be fixed automatically.

| Rule | Severity | Auto-fix |
|------|----------|----------|

Broken anchor fix

# Before (broken)
See [Installation](#instalation) for setup steps.

# Heading in file
## Installation

# After (corrected)
See [Installation](#installation) for setup steps.

Markdownlint Rules Reference

Command: npx --yes markdownlint-cli2 <filepath>