Module rule_priority 

Layer priority for CssRuleBlock. Lower numbers cascade first; higher numbers override earlier layers at the same specificity.

u8 leaves 256 slots, so a new layer can be inserted between any two existing slots without renumbering consumers. The gaps between named slots are intentional — fill them with custom intermediate layers if/when @layer lands.

Constants

AUTHOR

Default for parser-produced rules: the app author’s CSS. Everything coming out of Css::from_string lives here.

INLINE

Inline style="..." / NodeData::set_css(...) rules — used once the inline-vs-component unification (separate plan) folds inline storage into the same Vec.

RUNTIME

Reserved for direct-rule runtime overrides. Today the prop_cache handles runtime overrides via user_overridden_properties; this slot is reserved so a future “push a CssRuleBlock at runtime” path stays above inline. Used only when a callback writes a full rule, not a single property.

SYSTEM

Stylesheets the host system reports (system fonts, theme CSS derived from SystemStyle). One step above UA so they win against framework defaults but lose against anything the app author writes.

UA

User-Agent / framework defaults. Widget code that emits its own default CSS uses this. Lowest priority — anything else overrides it.