TINYDOC-3494 - Add guidance for disabling or stripping HTML formatting

[kemister85]

Ticket: TINYDOC-3494

Site: Staging

Changes

Closes a documentation gap where users searching for how to disable or strip HTML formatting could not find direct guidance. The relevant configuration options (valid_elements, invalid_elements, extended_valid_elements, paste_as_text) already exist on the Content filtering page, but there was no worked guidance for restricting or stripping formatting, and no path to it from the Content formats page where these users typically land.

• modules/ROOT/pages/content-filtering.adoc — Added a new "Disabling or stripping HTML formatting" section that:
  • Explains, at a behavioral level, that content is validated and cleaned against a schema when it is set, pasted, or retrieved, and that anything outside the schema is removed.
  • Describes what each option does (valid_elements replaces the allowed set, extended_valid_elements adds to it, invalid_elements removes named elements) and links each option mention to its section anchor on the page.
  • Clarifies that of the three options only valid_elements and invalid_elements restrict content, while extended_valid_elements widens the default schema and is therefore not a stripping mechanism, with a pointer to its option description lower on the page.
  • Notes that when a stripped element is a block element, the text it contained is rewrapped in the block element set by forced_root_block (p by default), so a removed <h1> is returned as a <p>.
  • Provides three worked examples: restricting content to an allowed subset with valid_elements, removing specific formatting with invalid_elements, and stripping all formatting from pasted content with paste_as_text.
  • Cross-references the Schema and DomParser API reference pages and the Content formats page.
• modules/ROOT/pages/content-formatting.adoc — Added a pointer from the Content formats page to the new guidance so users looking to restrict or strip formatting are directed to the correct page.

Validation

• Option behavior verified against tinymce source (core/main/ts/api/html/Schema.ts, DomParser.ts).
• Root block rewrapping verified against DomParser.ts (addRootBlocks, called for root content after filtering) and the forced_root_block default of p in core/main/ts/api/Options.ts.
• Guidance describes option behavior only; no internal implementation functions are referenced.
• Local Antora build passes with no warnings for the changed pages; all cross-references resolve (option section anchors including forced_root_block, apis/tinymce.html.schema, apis/tinymce.html.domparser, copy-and-paste#paste_as_text, content-filtering#disabling-or-stripping-html-formatting).

Prepared for documentation team review.