xmp element

<xmp> was a shortcut for showing HTML source on a page: everything between <xmp> and </xmp> appears as typed, in a monospace font, with no need to escape angle brackets. MDN traces it to HTML 2, and it still turns up in old pages.

Why avoid

It is obsolete. The HTML Standard lists xmp among the elements that “are entirely obsolete, and must not be used by authors”, with the instruction: “Use pre and code instead, and escape < and & characters as < and & respectively.”

The convenience comes with limits that are easy to trip over. The parser handles <xmp> with “the generic raw text element parsing algorithm”, which switches the tokenizer to the RAWTEXT state. In that state nothing is markup, and that includes character references: the tokenizer only watches for <, to find the end tag. Two things follow:

• Character references show up literally. Writing & inside xmp displays the five characters &, not an ampersand, so there is no way to write a character you can’t type.
• The content can never contain </xmp>. The first </xmp ends the element, so a page can’t use xmp to show markup that itself mentions xmp.

What remains is appearance. The rendering section styles it exactly like pre: display block, margin-block: 1em, and font-family: monospace; white-space: pre. It says nothing about what the content is. The HTML Accessibility API Mappings give code the WAI-ARIA code role, and xmp no role at all.

Use instead

Wrap the sample in pre and code, and escape < and &:

<pre><code>&lt;p class="note"&gt;Tom &amp; Jerry&lt;/p&gt;</code></pre>

Detectability

Fully detectable by tag name. deadhead never lints the content of an xmp, because a browser reads it as text, so only the element itself is reported. There is no autofix: removing it would delete the content, and moving to pre and code means renaming the element and escaping its content, which a fix can’t do.

Resources

• HTML Standard — Non-conforming features — xmp is obsolete; use pre and code with < and & escaped instead.
• HTML Standard — Parsing: the “in body” insertion mode — xmp uses the generic raw text element parsing algorithm, whose RAWTEXT state decodes no character references.
• HTML Standard — Rendering: flow content — xmp is displayed like pre: block, monospace, white-space: pre.
• W3C — HTML Accessibility API Mappings — code maps to the ARIA code role.
• MDN — <xmp> — deprecated since HTML 3.2, “not implemented in a consistent way”; use pre or code.