HTML5 MathML
HTML5 MathML <merror> Tag
The <merror> tag displays the contents of an error message, typically emitted by a MathML processor when it cannot interpret markup. It renders its children with an error style (often a red box).
Definition and usage
The <merror> element is a container for a message that highlights a syntax or processing error in a formula. Authoring tools and preprocessors wrap invalid input in <merror> so the reader sees something went wrong instead of a silently broken equation.
Syntax
<merror>
<mtext>error message</mtext>
</merror>Example
<math>
<merror>
<mtext>Syntax error: unexpected token</mtext>
</merror>
</math>The message inside <merror> is displayed with a distinct, usually boxed and coloured, appearance so it stands out from valid mathematics.
ℹ️
As part of MathML Core, <merror> is supported by modern browsers. It is mainly generated by tools rather than hand-written by authors.