Return type: Switch
Returns:       True if the attribute has no set value, false otherwise.

Syntax

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

An attribute test that succeeds when the referenced element or data attribute has no set value, either in the start tag or in the element declaration. Otherwise, the test fails. Using isnt instead of is reverses the results.

For example:

  repeat over attributes as this-one
     do when attribute this-one isnt implied
        output key of attribute this-one ||
        "='%v(this-one)'%n"
     done
  again

Unlike most other attribute references, no error occurs if the specified attribute doesn't 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 the specified attribute is not declared, the is form of the test always fails, and the isnt form always succeeds.

Related Syntax attribute attributes

Related Concepts Attribute tests on items of the "attributes" shelf

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