STR-009 Hard constraint layer: document

Maintain heading hierarchy

IF heading levels skip or reflect visual size rather than logical nesting, THEN repair the hierarchy ELSE retain.

Why the rule exists

Assistive technology and scanning readers depend on a coherent outline.

Condition

The rule fires when this evaluates true. Paths marked below must be present in the fact base; the engine reports the rest rather than guessing them.

ANY
- document.heading_level_skip eq true
- document.headings_used_for_visual_style eq true

Facts this rule reads

Fact paths read by STR-009 and whether the analyser derives them
Path	Source
`document.heading_level_skip`	You supply it
`document.headings_used_for_visual_style`	You supply it

Then

restructure — target document.heading_tree
separate — target presentation_from_semantics

Else

retain — target current_text, No triggering condition is present.

LAKA

Smallest sufficient intervention

Yes

Primary axes

Sources

Writing for Web Accessibility — W3C Web Accessibility Initiative link
Clear structure, descriptive labels, alternatives, and understandable content.
Web Content Accessibility Guidelines 2.2 — W3C link
Testable accessibility requirements for web content.

The raw rule record

Verbatim from 10-paragraph-document-rules.json. Also available at /v1/rules/STR-009.

{
  "id": "STR-009",
  "name": "Maintain heading hierarchy",
  "domain": "structure",
  "layer": "document",
  "strength": "hard_constraint",
  "human_logic": "IF heading levels skip or reflect visual size rather than logical nesting, THEN repair the hierarchy ELSE retain.",
  "when": {
    "any": [
      {
        "path": "document.heading_level_skip",
        "operator": "eq",
        "value": true
      },
      {
        "path": "document.headings_used_for_visual_style",
        "operator": "eq",
        "value": true
      }
    ]
  },
  "then": [
    {
      "action": "restructure",
      "target": "document.heading_tree",
      "require": "logical_nesting"
    },
    {
      "action": "separate",
      "target": "presentation_from_semantics"
    }
  ],
  "else": [
    {
      "action": "retain",
      "target": "current_text",
      "reason": "No triggering condition is present."
    }
  ],
  "unless": [],
  "because": "Assistive technology and scanning readers depend on a coherent outline.",
  "diagnostics": [],
  "examples": {},
  "source_ids": [
    "WEB-005",
    "WEB-007"
  ],
  "laka": {
    "smallest_sufficient_intervention": true,
    "primary_axes": [
      "scope",
      "depth",
      "magnitude",
      "reversibility"
    ]
  }
}