What Is Wrong with My "checked" Attribute Values?

Attribute "checked" is an optional attribute for HTML element "input". In XHTML specification, attribute "checked" has only one predefined value: "checked". However, in HTML specification, attribute "checked" requires no value.

If you are converting existing HTML documents to HTML format, you will get some syntax error on your pre-selected items in radio buttons, check boxes and dropdown lists, "checked" attributes are used without any values.

Here are some interesting examples of "checked" attributes:

• <input type="radio" name="lang" value="HTML" checked> - Invalid, all attributes must have values. This is valid as HTML documents.
• <input type="radio" name="lang" value="HTML" checked="yes"> - Invalid, "yes" is not the predefined value of attribute "checked".
• <input type="radio" name="lang" value="HTML" checked="checked"> - Valid, attribute "checked" is assigned with predefined value "checked".

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