operator
is with isnt will reverse the results. referents (has | hasnt) key string-expression
A test to see if a particular referent exists within the current referents scope.
The string expression is the string giving the name of the referent. This test succeeds if one of the items in the referents shelf has a name equal to string-expression, and fails otherwise. hasnt will reverse the results of the test.
A referent will have an entry on the referents shelf if it has been:
set referent), or
silent-referent).