HTML tag support tracker

This issue tracks which Html tags are supported (both parsed and displayed fully correctly) in rich Html message content.

For more info, see the list of supported Html tags and attributes in the Matrix spec the newest v1.13 spec's list of supported Html tags and attributes.

• Headers: h1, h2, h3, h4, h5, h6
• b, strong: bold
• i, em: italic/emphasis
• u: underline
• del/strike: strikethrough/cross-out
• p: paragraph
• hr: horizontal rule, separator
• br: line break, new line
• blockquote
• ul
• ol
  • start
• li
• pre: code blocks
  • class="language-*" for syntax highlighting
    • This is blocked on Makepad's upcoming support for syntax highlighting
• code: inline code
• font
  • color
  • data-mx-color
  • data-mx-bg-color
• span
  • data-mx-bg-color
  • data-mx-color
  • data-mx-spoiler: #274
• a: hyper links
  • href
    • Note: href value must not be relative, must have a scheme matching one of: https, http, ftp, mailto, magnet
    • web clients should add a `rel="noopener"``attribute
  • name — this is explicitly not supported
  • target — this is explicitly not supported
• sup
  • Fixed/improved by https://github.com/makepad/makepad/pull/1051
• sub: is parsed correctly, but doesn't always display properly
  • Fixed/improved by https://github.com/makepad/makepad/pull/1051
• div: i think this is only used for the new latex math feature (which we need to support in span too)
• table: implemented by https://github.com/makepad/makepad/pull/1032
  • caption -- a table caption
  • thead -- a table header (the first row, typically column labels)
  • tbody -- a table body (rows that come after the thead table header)
  • tr -- a table row
  • th -- a table column header (the left-most cell in a row)
  • td -- a table data cell
  • Fixed/improved by https://github.com/makepad/makepad/pull/1051
• img: inline images
  • width
  • height
  • alt
  • title
  • src
• details: an expandable view that shows a summary when closed and the full content when open.
  • summary: the short content viewable when details is closed.
  • Implemented: https://github.com/makepad/makepad/pull/1052
• mx-reply: see issue https://github.com/project-robius/robrix/issues/82