Use when reviewing image assets, markup, and CDN or build transforms related to Use <picture> with an <img> fallback. Check encoded size, rendered size, loading strategy, and above-the-fold impact together.
Installation
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Use when reviewing image assets, markup, and CDN or build transforms related to Use <picture> with an <img> fallback. Check encoded size, rendered size, loading strategy, and above-the-fold impact together.
A <picture> without an <img> fallback renders nothing in browsers that don't support <picture> (IE11) or don't support any of the <source> formats. The <img> child is also where alt, width, height, loading, and fetchpriority attributes live—these apply regardless of which source the browser selects.
Quick Reference
Every <picture> must end with an <img> element—it is the required fallback and carries alt
<source> elements are evaluated top-to-bottom; the first match wins
Use type="image/avif" and type="image/webp" on <source> for format selection
The <img src> should point to a JPEG or PNG—the universal fallback for all browsers
Check
Scan all elements in this codebase. Verify: 1) Every has an as its last child (required fallback). 2) The has an alt attribute. 3) The has width and height attributes. 4) elements appear before the child. 5) Each has either a srcset attribute or a media attribute. 6) format-selecting elements have a type attribute (type="image/avif", type="image/webp"). Flag any missing an child or with not as the last child.
Fix
For each element with issues: 1) If missing : add as the last child. 2) If is not last: move it to after all elements. 3) If elements lack type attributes for format selection: add type="image/avif" or type="image/webp". 4) Verify the points to a universally supported format (JPEG or PNG) as the ultimate fallback. Show the corrected markup.
Explain
Explain how the element works. Browsers evaluate elements in document order and use the first one whose conditions match (type, media, srcset). The element is the fallback for browsers that don't support (IE11) or don't support the source format. Without an child, is invalid HTML and produces no output. The alt attribute must be on the , not the elements—it applies regardless of which source is selected.
Code Review
Review image assets, markup, and delivery configuration related to Use with an fallback. Flag exact files or components where format choice, sizing, or loading behavior violates the rule, and describe how to confirm the fix in DevTools.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
