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HTML
- use semantic markup
- use ARIA roles for unsemantic markup, e.g. search field
- alt tags in content media, e.g. images, video, audio, etc.
- empty alt tags in decorative media content, e.g. images, etc.
CSS
- color contrast ratio
- use not only color to distinguish function, e.g. text, icon, etc.
- preference media queries, e.g. dark mode, reduced motion, color contrast, etc.
- use
:focus(-within)along:hoverfor showing elements, e.g. dropdown, tooltip, etc.
JavaScript
- in SPA after client-side routing put focus on top of page, read title
Browser support
- define data driven cut-off point, when income due to these customers doesn’t warant cost of support anymore
- define cut-off point relative instead of absolute, e.g. at most last N versions of a non-dead browser with more than X% market share
- show update warning below cut-off point, don’t break silently, e.g. fullscreen message
- browser detection based on HTTP User Agent Hint headers, deliver minimal page with update warning instead of whole page
- beware: as of 2020 HTTP User Agent Hints are still only a proposal, see Improving user privacy and developer experience with User-Agent Client Hints