diff --git a/src/lib/builtins.pl b/src/lib/builtins.pl
index bea783f77..1be332503 100644
--- a/src/lib/builtins.pl
+++ b/src/lib/builtins.pl
@@ -33,6 +33,14 @@
 internal settings and basic I/O are all here.
 */
 
+%% :(+M, +T)
+%
+% Explicit module qualification operator. True if T succeeds when called in the context of module M.
+% This calling context determines how predicates resolve to user-defined procedures.
+% The context is flat. That is, in the goal `M2:M1:T`, predicate lookups are performed only in M1 and not M2.
+% 
+% Consider carefully before using explicit module qualification.
+% Prefer meta-predicate declarations when possible.
 
 % unify.