The Old NetISSUE #12 of 60

xhtml validation · the strict parser

Pixel PeteVSQuirks Mode

Pixel Pete saysXHTML validation runs a page through a strict parser/validator that reports every error.

Because XHTML is XML, you can validate it with the W3C validator or any XML parser — they flag unclosed tags, bad nesting, unquoted attributes, and DTD violations precisely. This was a selling point: deterministic error reporting. The downside in production was that real browsers in XML mode would refuse to render an invalid page at all.

Power-ups you unlock

Validate with the W3C validator / XML parsers
Precise, deterministic error reports
Catches nesting, quoting, DTD issues
XML mode refuses to render invalid pages

Quirks Mode attacks — common mistakes

Skipping validation and shipping broken XML
Validating against the wrong DTD
Assuming browsers will recover in XML mode

Boss battleList three errors an XHTML validator would catch that HTML tolerates.

Example code

<!doctype html><html><head><meta charset="utf-8"></head>
<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre>validator flags:
  · unclosed &lt;li&gt;
  · &lt;DIV&gt; uppercase
  · width=100 unquoted</pre></body></html>

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