Document backdrop root concept on backdrop-filter page#43421
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Document backdrop root concept on backdrop-filter page#43421
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Add a Description section explaining that backdrop-filter effects are bounded by the nearest ancestor backdrop root, and list the properties that create a backdrop root (filter, opacity, mask, clip-path, backdrop-filter, mix-blend-mode, will-change). This is a common source of confusion when backdrop-filter appears to have no effect. Fixes mdn#40602
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Summary
backdrop-filterCSS property page explaining that effects are bounded by the nearest ancestor backdrop rootfilter,opacity,mask,mask-image,mask-border,clip-path,backdrop-filter,mix-blend-mode, andwill-changebackdrop-filterappears to have no effect due to an ancestor backdrop rootMotivation
Developers are frequently confused when
backdrop-filterdoesn't affect all pixels behind an element. The concept of a "backdrop root" (from Filter Effects Level 2) is not documented on MDN. A previous PR (#40627) attempted this but was closed due to merge conflicts; this is a fresh implementation incorporating reviewer feedback (using a dedicated Description section instead of a note).Fixes #40602.
Test plan