Reads the runtime value of the attribute if it caqn produce one. The result is returned as a Variant object.
Ditto, but also accepts a template parameter which the result is converted to (if the conversion is possible).
Checks if this attribute is expression. Any attribute that can produce a value at runtime is considered an expression attribute.
Checks if this attribute is a type (or some other non-expression).
Represents a single attribute attached to some element.