Draggable: Scope the clone's fallback z-index to non-slot placements#78354
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The compat overlay slot already supplies an isolated stacking context, so the clone's legacy `z-index: 1000000000` was leaking into intra-slot ordering — biasing the clone above any other slot residents (e.g. `@wordpress/ui` portals opened mid-drag) for no architectural reason. Tag the clone with an `is-in-compat-slot` modifier when it lands in the slot, and reset its `z-index` from CSS. Fallback placements (non- WP hosts, cross-document drags) keep the legacy value.
Apply the legacy `z-index` only when the clone is NOT in the compat slot, rather than setting it and overriding it inside the slot.
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mirka
approved these changes
May 15, 2026
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What?
Follow up to #78183. Drop the drag clone's legacy
z-indexwhen it lands inside the@wordpress/uicompat overlay slot. Addresses this review comment.Why?
The compat slot already supplies an isolated stacking context. Inside it, the legacy
z-indexonly biases intra-slot ordering — currently pinning the clone above other slot residents (e.g.@wordpress/uiportals from #78095). Letting DOM order decide is the more conservative default.More on the stacking interaction
The compat slot in
@wordpress/uiisposition: fixed; z-index: 1000000003; isolation: isolate. Inside it, any positivez-indexresolves only against siblings inside the slot. The clone's legacyz-index: 1000000000was originally chosen to compete with the page; carrying it into the slot was an opinionated stacking choice we never explicitly made.For the fallback paths (non-WP hosts, cross-document drags) the legacy
z-indexstill applies — those placements have to compete with the rest of the page.How?
Add an
is-in-compat-slotmodifier class on the clone wrapper when (and only when)compatSlotis non-null, and gate the fallbackz-indexrule with:not(.is-in-compat-slot).Why a modifier class rather than a structural CSS selector?
The CSS-only alternative would be
[data-wp-compat-overlay-slot] > .clone { z-index: auto; }. That works, but it couples the override to the slot's DOM relationship; the modifier-class approach keeps the conditional styling intent at the JS call site (where thecompatSlotbranch already lives) and the CSS rule self-contained.Testing Instructions
npm run storybook:dev) → Playground / Debug fixtures / Draggable cross-document fallback → drag inside the iframe; clone still renders with the legacy z-index.@wordpress/uitooltips/portals continue stacking above@wordpress/componentsoverlay hosts.[data-wp-compat-overlay-slot]above other overlays.Use of AI Tools
Cursor + Claude 4.7