Tag Tree

The hierarchical structure of semantic tags embedded within a PDF document that defines the logical organization and reading order of its content. A tag tree is analogous to the DOM (Document Object Model) in HTML — it identifies headings, paragraphs, lists, tables, figures, and other structural elements, allowing assistive technologies like screen readers to navigate the document meaningfully rather than reading raw text in visual layout order. A well-formed tag tree includes a root Document element, properly nested heading levels (H1-H6), semantic tags for paragraphs (P), lists (L, LI), tables (Table, TR, TH, TD), and figures with alternative text. Decorative elements should be marked as artifacts to be skipped by screen readers. The tag tree is the foundation of PDF accessibility — without it, a PDF is essentially inaccessible to screen reader users.