Lua Filters Reference¶

Pandoc Lua filters inject accessibility metadata into output formats during conversion.

accessibility.lua (HTML)¶

Adds ARIA attributes for screen readers.

Image Handler¶

function Image(img)

Attribute	Value	Purpose
`aria-description`	`longdesc` value	Extended description for screen readers
`accessibility-description`	`longdesc` value	Redundant for compatibility
`title`	Caption text	Tooltip and accessible name
`alt`	Caption or empty	Fallback alt text

Link Handler¶

function Link(link)

Sets aria-label from the link's title attribute.

Div Handler¶

function Div(div)

For divs with class image-description, ocr-text, or ui-controls:

Attribute	Value
`aria-hidden`	`true`
`role`	`note`

These divs are marked as supplementary notes, not primary content.

Header Handler¶

function Header(header)

Sets aria-level to the heading level (1-6).

docx-accessibility.lua (DOCX)¶

Identical to the HTML filter. Injects the same ARIA attributes into the DOCX OpenXML structure.

pdf-accessibility.lua (PDF)¶

Enhanced filter for PDF/UA compliance. Adds explicit PDF tags and metadata.

Image Handler¶

function Image(img)

Attribute	Value	Purpose
`pdf-alt`	First 150 chars of `longdesc`	Short Alt entry
`pdf-tag`	`Figure`	Explicit PDF structure tag
`pdf-longdesc`	Full `longdesc`	Expanded `/E` description
`alt`	Caption or empty	Fallback alt text

Header Handler¶

function Header(header)

Sets pdf-tag to H1, H2, etc. based on heading level.

Para Handler¶

function Para(para)

Sets pdf-tag to P for all paragraphs.

List Handler¶

function List(list)

Sets pdf-tag to L for all lists (bullet and numbered).

BlockQuote Handler¶

function BlockQuote(block)

Sets pdf-tag to BlockQuote.

CodeBlock Handler¶

function CodeBlock(code)

Sets pdf-tag to Code.

Table Handler¶

function Table(table)

Sets pdf-tag to Table.

Meta Handler¶

function Meta(meta)

Injects PDF/UA metadata:

meta["pdf-metadata"] = {
    producer = "Folge Vision Pipeline - PDF/UA Compliant",
    creator = "Documentation Team",
    subject = "Accessible Software Documentation",
    keywords = "documentation,accessibility,software,PDF/UA,WCAG,ARIA",
    pdf_version = "1.7",
    tagged = true,
    conforms_to = "PDF/UA-1"
}

Custom Filters¶

To create a custom filter, follow the Pandoc Lua filter API:

function MyElement(element)
    element.attributes["my-attribute"] = "my-value"
    return element
end

Place the .lua file in the project root and reference it with --lua-filter=my-filter.lua.