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operator	attribute is specified
	Related Syntax

Summary

Boolean A value of true when the attribute has a value; otherwise, false.

Syntax

  attribute attribute-name element-qualifier*
     ((item | @) numeric-expression)? (is | isnt) specified 

An attribute test that succeeds when the referenced:

• element attribute has a value specified in the start tag in the document instance or,
• data attribute has a value specified in the external entity declaration of the DTD.

The test fails otherwise. Using isnt instead of is reverses the results.

Unlike all other attribute references, no error occurs if the specified attribute does not exist, or was not given a value (since the test does not actually use the value).

If the element-qualifier references an element that does not exist, or if the specified attribute is not declared, the is form of the test always fails, and the isnt form always succeeds.