Related Syntax	Related Concepts
operator	is implied

Return type: Boolean
Returns:       

True when the attribute or data attribute has no value set, and false otherwise. Replacing is with isnt will reverse the results.

  attribute attribute-name element-qualifier*
     (indexer")? (is | isnt) implied

An attribute test that succeeds when:

• the reference element attribute has no value set, either in the start tag or in the element declaration
• the data attribute has no value set, either in the start tag or in the element declaration