A constraint definition assigns a name to the result of a constraint expression:
GettysburgAddress =
starts with
"Four score and seven years ago",
ends with
"shall not perish from the earth"
Region sets named by a constraint definition can be used in the same way as region sets named by a parser, as in the example Sentence at start of GettysburgAddress. A constraint system is a set of constraint definitions separated by semicolons.