TIP 72

What is HTML & CSS validation?

Validation is used to examine the markup in documents and report any errors found. Validators point out mistakes such as absent or incorrect tags and missing quotation marks; some validators will also warn of common style faults, such as failing to provide ALT text for images.

Why validate?

Many bowsers are non-standars compliant and are deliberately designed to recover from errors in markup. In one way this is very good for beginner designers, because it often means that even badly marked up documents are viewable.

You cannot be sure how different browsers (or even different versions of the same browser) will recover from a particular error. Validation will help future-proof your documents and is professional website design best practice.

In Summary

• Validate your documents now to minimize the risk of an inaccessible website

Where can I validate my documents?

HTML checkers come in two types:

• Validators, or SGML parsers, which check documents against a DTD (Document Type Definition - the set of rules which defines the syntax of the language)

• Lint or rules-based programs, which scan the documents looking for errors; in addition to finding mistakes such as missing, mismatched, incorrectly nested, or invalid tags, these will often warn you of common style problems.

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