attribute is implied

operator

Return type:
Switch
Returns:
Returns true when the attribute has no set value, and false otherise. Replacing is with isnt reverses the result.
Syntax
attribute attribute-name (of element-expression)? (is | isnt) implied


Purpose

The is implied attribute type test 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 a
     output key of attribute a || "=%"%v(a)5"%n"
        when attribute a isnt implied
  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-expression 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
Related Concepts