DOC-5931 "hierarchy" diagram hook

build/render_hook_docs/HIERARCHY_FORMAT.md

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+# Hierarchy Format Guide
+
+This document describes the YAML-based format for representing hierarchies (class inheritance, filesystem trees, etc.) in Redis documentation.
+
+## Overview
+
+Hierarchies are written in YAML format within a code block with the language identifier `hierarchy`. The render hook preserves the YAML source for AI agents while JavaScript generates a visual diagram for users.
+
+## Basic Syntax
+
+### Simple Hierarchy
+
+```yaml
+Parent:
+    Child1:
+    Child2:
+        Grandchild1:
+        Grandchild2:
+```
+
+This represents:
+```
+Parent
+├── Child1
+├── Child2
+│   ├── Grandchild1
+│   └── Grandchild2
+```
+
+### Quoted Names
+
+Use quotes for names containing special characters (spaces, punctuation, etc.):
+
+```yaml
+"Top-level folder":
+    "file1.js":
+    "file2.png":
+    "Inner folder":
+        "file3.jpg":
+```
+
+This is especially important for:
+- Filenames with extensions (`.js`, `.png`, etc.)
+- Names with spaces
+- Names with hyphens or other punctuation
+
+## Metadata
+
+Add metadata to any item using the special `_meta` key:
+
+```yaml
+"Exception":
+    _meta:
+        description: "Base exception class"
+    "RuntimeException":
+    "IOException":
+```
+
+Currently supported metadata fields:
+- `description`: A brief description of the item (displayed as italic text after the item name)
+- `ellipsis`: Boolean indicating this is a placeholder for omitted items
+
+## Ellipsis (Omitted Items)
+
+Use an ellipsis item to indicate that some items are not shown:
+
+```yaml
+"RedisError":
+    "ConnectionError":
+    "ResponseError":
+    "InvalidResponse":
+    "...":
+        _meta:
+            ellipsis: true
+            description: "Other exception types"
+```
+
+The `_meta` with `ellipsis: true` tells the renderer to display this as "..." and not expand it further. The ellipsis item is rendered with a dotted vertical line below it to indicate continuation. You can optionally add a `description` to provide context about the omitted items.
+
+## Complete Example: Exception Hierarchy
+
+```yaml
+"RedisError":
+    _meta:
+        description: "Base class for all redis-py exceptions"
+    "ConnectionError":
+        _meta:
+            description: "Connection-related errors"
+        "TimeoutError":
+        "BusyLoadingError":
+    "ResponseError":
+    "InvalidResponse":
+    "DataError":
+    "PubSubError":
+    "...":
+        _meta:
+            ellipsis: true
+            description: "Other exception types"
+```
+
+This represents an exception hierarchy with:
+- A base exception class with description
+- Nested exception types
+- An ellipsis indicating additional exception types not shown
+
+## Complete Example: Filesystem Hierarchy
+
+```yaml
+"(root)":
+    "config.yaml":
+        _meta:
+            description: "Main configuration file"
+    "jobs":
+        _meta:
+            description: "Folder containing job definitions"
+        "default-job.yaml":
+            _meta:
+                description: "Default job configuration"
+        "job1.yaml":
+        "...":
+            _meta:
+                ellipsis: true
+                description: "Other job files"
+```
+
+This represents a filesystem structure with:
+- A root folder containing configuration files
+- Nested directories and files
+- Descriptions for each item
+- An ellipsis indicating additional files not shown
+
+When `type="filesystem"` is used, the renderer displays file and folder icons next to each item.
+
+## Usage in Markdown
+
+### Code Block Syntax
+
+~~~
+```hierarchy {type="filesystem"}
+Parent:
+    Child1:
+    Child2:
+```
+~~~
+
+### Attributes
+
+- `type` (optional): Indicates the kind of hierarchy. Common values:
+  - `type="exception"` - Exception/error hierarchy
+  - `type="filesystem"` - Filesystem or directory structure
+  - `type="generic"` - Generic hierarchy (default if omitted)
+
+  The type helps the renderer apply appropriate styling and helps AI agents understand the context.
+
+- `noicons` (optional): Disables icon rendering for filesystem hierarchies. Use `noicons="true"` to hide file/folder icons.
+  - Only applies to `type="filesystem"`
+  - Default: icons are shown
+
+### Placement
+
+Place the hierarchy code block where you want the diagram to appear in the rendered HTML. The render hook will:
+1. Preserve the YAML source in a `<pre>` element (for AI agents)
+2. Generate a visual diagram below it (for users with JavaScript)
+
+## Best Practices
+
+### Naming
+
+- Use clear, descriptive names
+- Use quotes for any names with special characters
+- Keep names concise but meaningful
+
+### Organization
+
+- Order items logically (alphabetically, by importance, etc.)
+- Use ellipsis to indicate omitted items rather than showing everything
+- Group related items together
+
+### Metadata
+
+- Add metadata only when it provides useful information
+- Use consistent metadata field names across similar hierarchies
+- Keep descriptions brief (one sentence)
+
+## Metadata Reference
+
+### Supported Fields
+
+| Field | Type | Purpose | Example |
+|-------|------|---------|---------|
+| `description` | string | Brief description of the item (displayed as italic text) | `"Base exception class"` |
+| `ellipsis` | boolean | Marks as placeholder for omitted items | `true` |
+
+### Notes
+
+- The `description` field is displayed as italic text after the item name in the rendered diagram
+- The `ellipsis` field should be set to `true` for items representing omitted content (typically named `"..."`)
+- Other metadata fields may be added in the future
+
+## Rendering
+
+### For Users (HTML)
+
+The render hook generates a visual SVG diagram with:
+- ASCII art-style tree structure with indented text
+- Connected tree lines showing parent-child relationships
+- File and folder icons for filesystem hierarchies (when `type="filesystem"`)
+- Descriptions displayed as italic text after item names
+- Dotted vertical lines for ellipsis items indicating continuation
+- Space Mono font matching Redis documentation style
+
+### For AI Agents (Markdown)
+
+AI agents accessing the `.html.md` version see the raw YAML:
+- Clean, structured format
+- Easy to parse and understand
+- Metadata preserved for context
+- Descriptions available for understanding item purposes
+
+## Validation
+
+The YAML must be valid according to the YAML 1.2 specification:
+- Proper indentation (spaces, not tabs)
+- Quoted strings for special characters
+- Valid YAML syntax
+
+Invalid YAML will cause rendering errors. Use a YAML validator to check your syntax.
+
+## Real-World Examples
+
+See the following files for real-world examples:
+- `content/develop/clients/redis-py/error-handling.md` - Exception hierarchy with descriptions
+- `content/integrate/redis-data-integration/data-pipelines/_index.md` - Filesystem hierarchy with file/folder icons
+