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SUPPORTED_HTML.md

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Supported HTML Elements and CSS Properties

This document lists the HTML elements and CSS properties that hyper_render renders correctly. Anything not listed here is either silently unwrapped (unknown tags) or ignored (unknown CSS properties).

For content that falls outside this subset, use the fallbackBuilder parameter to delegate to a WebView or other renderer — see LIMITATIONS.md for guidance.

Block Elements

Element Notes
<p> Paragraph with margin collapse
<div>, <section>, <article> Generic block containers
<header>, <footer>, <nav>, <aside> Semantic sections
<h1>–<h6> Headings with default sizing
<blockquote> Indented quotation
<pre> Preserves whitespace (white-space: pre)
<hr> Horizontal rule
<ul>, <ol> Unordered and ordered lists
<li> List items (9 list-style-type values)
<dl>, <dt>, <dd> Description lists
<table>, <thead>, <tbody>, <tfoot> Table structure
<tr> Table row
<th>, <td> Table cells; colspan and rowspan supported
<caption> Table caption
<details>, <summary> Collapsible disclosure widget
<figure>, <figcaption> Figure with caption

Inline Elements

Element Notes
<span> Generic inline container
<a> Links — href resolved against baseUrl; onLinkTap callback
<strong>, <b> Bold
<em>, <i> Italic
<u> Underline
<s>, <del> Strikethrough
<ins>, <mark> Highlight
<code>, <kbd>, <samp>, <var> Monospace
<sub>, <sup> Subscript / superscript (basic positioning)
<small>, <q>, <cite>, <abbr> Semantic inline
<time> Date/time
<br> Line break
<ruby>, <rt>, <rp> CJK ruby annotations (furigana)

Replaced / Atomic Elements

Element Notes
<img> Lazy-loaded; alt, width, height, aspect ratio
<video> Placeholder widget with poster image; no JS playback
<audio> Placeholder audio bar
<source> Parsed for media attributes
<picture> First <img> child used

CSS Properties

Text

Property Support
color Full — named, hex (#RGB, #RRGGBB, #RGBA, #RRGGBBAA), rgb(), rgba(), hsl()
font-size px, em, rem, %, named (small/medium/large/…)
font-weight Numeric (100–900) and named
font-style normal, italic, oblique
font-family System font lookup
line-height Unitless, px, em, %
letter-spacing px, em
word-spacing px, em
text-align left, right, center, justify
text-decoration underline, line-through, overline, none
text-transform uppercase, lowercase, capitalize
white-space normal, pre, pre-wrap, nowrap
text-overflow clip, ellipsis
direction / dir attr ltr, rtl

Box Model

Property Support
width, height px, %, em, rem; auto
min-width, max-width px, %, em
margin All shorthand forms; auto on block elements
padding All shorthand forms
border border, border-width, border-color, border-style
border-style solid, dashed, dotted, double, none
border-radius px, %
box-sizing border-box, content-box
overflow visible, hidden

Layout

Property Support
display block, inline, inline-block, none, flex, grid
float left, right, none
clear left, right, both, none
position relative only — absolute/fixed not supported
Flexbox flex-direction, justify-content, align-items, flex-wrap, flex, flex-grow, flex-shrink, flex-basis
CSS Grid display: grid, grid-template-columns, grid-template-rows, gap, grid-column, grid-row

Background

Property Support
background-color Full color support
background-image url(), linear-gradient()
background-size cover, contain, fill
background-position Not supported

Effects

Property Support
opacity Full (0.0–1.0)
box-shadow x y blur spread color (multiple shadows)
text-shadow x y blur color (multiple shadows)
filter blur, brightness, contrast
backdrop-filter blur (Glassmorphism)
transform Not supported
clip-path Not supported

Advanced

Property Support
CSS Variables (--prop: value) Full — var() with fallback
calc() px/em/rem arithmetic
!important Respected in cascade
CSS specificity Full — inline > id > class > element
@media queries Not supported
@keyframes Not directly — use HyperAnimatedWidget

HTML Attributes

Attribute Elements Notes
id, class All Used for CSS selectors
style All Inline CSS
lang, dir All Language and text direction
href <a> Absolute or relative (resolved via baseUrl)
src, alt, width, height <img>, <video>, <audio> Media attributes
colspan, rowspan <td>, <th> Table spanning
open <details> Default expanded state
controls, autoplay, loop, muted, poster <video>, <audio> Media controls
aria-label, aria-labelledby All Accessibility labels
role All ARIA role (button, region, heading)

Unsupported

The following will not render correctly in hyper_render. Use fallbackBuilder to delegate to a WebView when the content requires these:

  • position: absolute / position: fixed — overlapping layouts
  • z-index — stacking contexts
  • clip-path — non-rectangular masks
  • @media queries — responsive breakpoints
  • @keyframes / CSS animations (use HyperAnimatedWidget instead)
  • <canvas> — requires JavaScript 2D/WebGL
  • <form>, <input>, <select>, <textarea> — interactive form controls
  • <script> — JavaScript execution is not supported
  • <iframe>, <embed>, <object>, <applet> — embedded content

Last updated: March 17, 2026