Describe image conversion validation failures precisely
The practical problem
A WebP tool that displays only a red border or a generic Error 400 leaves users guessing what needs fixing.
Implementation protocol
Associate the message with the invalid field and use an accessible live region. Explain allowed types and file-size limits without echoing untrusted HTML.
Worked scenario
Use 'Unsupported image: select PNG, JPEG or WebP under 10 MB' rather than relying on a red outline or obscure parser code.
What could go wrong
Sanitize any displayed filename and use textContent for untrusted material.
Acceptance criteria
Test corrupted files, enormous dimensions and keyboard navigation.
Source material and evidence boundaries
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