Unlike the other Fabl datatypes,the datatype id (also known as fabl:id) is is not defined by XML Schema Datatypes. Like strings, elements of id are sequences of characters. In XML Schema Datatype terminology, the value space of id is the same as that of string. The difference is that ids are immutable; there are no Fabl operations that modify the character sequence constituting an id. Id literals are surrounded by single quotes(''). Example:
'abc'; -->abc
Id literals do not make use of the backslash escape character, nor of the evaluation of expressions within angle brackets. Strings can be converted to ids with the following operator:
id toId(string s)
Equality (with == as alternative syntax) applies to ids:
boolean equal(id x,id y)
id coerces to string