<mark>
Text highlighted for contextual relevance — a search hit, a referenced passage.
Baseline: Widely available · Inline text semantics
When to use it
To mark why this passage matters right now: matched search terms, the line under discussion.
When not to
Not decoration and not emphasis — the highlight must answer 'relevant to what?'.
Example
…save the page for offline reading; there are no stylesheets…
<p>…save the page for <mark>offline reading</mark>; there are no stylesheets…</p>