6.1.1345
ENVIRONMENT?
environment-query
CORE
 
( c-addr u -- false | i * x true )

c-addr is the address of a character string and u is the string's character count. u may have a value in the range from zero to an implementation-defined maximum which shall not be less than 31. The character string should contain a keyword from 3.2.6 Environmental queries or the optional word sets to be checked for correspondence with an attribute of the present environment. If the system treats the attribute as unknown, the returned flag is false; otherwise, the flag is true and the i * x returned is of the type specified in the table for the attribute queried.

See:
A.6.1.1345 ENVIRONMENT?.

Rationale:
In a Standard System that contains only the Core word set, effective use of ENVIRONMENT? requires either its use within a definition, or the use of user-supplied auxiliary definitions. The Core word set lacks both a direct method for collecting a string in interpretation state (11.6.1.2165 S" is in an optional word set) and also a means to test the returned flag in interpretation state (e.g. the optional 15.6.2.2532 [IF]).
Testing:
\ should be the same for any query starting with X:
T{ S" X:deferred" ENVIRONMENT? DUP 0= XOR INVERT -> <TRUE>  }T
T{ S" X:notfound" ENVIRONMENT? DUP 0= XOR INVERT -> <FALSE> }T