The current query language is a bit awkward, but functional:
-query::= complex | simple | attr query.
-complex ::= operator query query.
+query ::= complex | simple | attr query.
+complex ::= operator query query.
operator ::= '@and' | '@or' | '@not'.
-simple ::= term | set.
-term ::= <word> | '"' <term> .. '"'.
-set ::= '@set' <setname>.
-attr ::= '@attr' <number> '=' <number>.
+simple ::= term | set.
+term ::= <word> | '"' <term> ... '"'.
+set ::= '@set' <setname>.
+attr ::= '@attr' <number> '=' <number>.
Eg.: