deadheadmeta http-equiv=X-UA-Compatible
X-UA-Compatible only ever controlled Internet Explorer document modes, and no shipping browser reads it.
- Avoid
- Unnecessary
- Severity
- UnnecessaryWorks, but is dead weight.
- Basis
- Vendor documentationOne vendor's documentation is the source.
- Detectable
- YesMatched exactly. Autofixable when the rule carries a fix.
- Matches
meta[http-equiv="X-UA-Compatible" i]Element rule, inside <head>.- Fix
- Removes the element
- Impacts
- Maintainability
- Related
script/type-javascript-mime
X-UA-Compatible was a Microsoft pragma, never a web standard. Internet Explorer 8
shipped with several document modes — emulations of the layout and scripting quirks of
IE 5, 7 and 8 — and picked one per page using heuristics, a compatibility list shipped by
Microsoft, and this pragma. IE=edge was the escape hatch: it told IE to stop guessing
and use its newest engine. Every HTML boilerplate of the era copied it, and it has been
copied forward ever since.
Why avoid
The pragma has had no reader since 2022. Internet Explorer 11 reached end of support on
15 June 2022 and its desktop application was permanently disabled; legacy (EdgeHTML)
Edge went out of support on 9 March 2021. Chromium-based Edge has one engine and no
document modes, so there is nothing for IE=edge to select.
It is also not inert in review. Because it looks like configuration, it invites cargo
cult edits — IE=edge,chrome=1 is still copied around, and the chrome=1 half asked for
Google Chrome Frame, a plugin discontinued in 2014. A line nobody can explain but nobody
dares delete costs more over a decade than the bytes it occupies.
Use instead
Delete it.
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>If you are serving the pragma as an HTTP response header rather than a <meta> tag,
delete that too — the same reasoning applies, and a header costs every response.
Detectability
Fully detectable. The pragma is a single element identified by one attribute value, with no context that changes the verdict, so a selector match is the whole rule and the fix is always to remove the element.
Resources
- HTML Standard — pragma directives — the normative list of
http-equivvalues;X-UA-Compatibleis not among them. - Internet Explorer 11 end of support — Microsoft, retired 15 June 2022.
- Specifying legacy document modes — Microsoft’s own documentation for what the pragma did.
This page is generated from content/rules/meta/http-equiv-x-ua-compatible.md, the same file the linter is built from. Think the rule is wrong, or that browsers moved on? Say so — that is the most useful issue you can file.