-query ::= ['@attrset' <attribute-set>] rpn
-rpn ::= complex | simple | attr rpn
-complex ::= operator rpn rpn
-operator ::= '@and' | '@or' | '@not' | '@prox' proximity
-simple ::= term | set.
-term ::= <word> | '"' <term> ... '"'.
-set ::= '@set' <setname>.
-attr ::= '@attr' [<attribute-set>] <number> '=' <number>.
-proximity ::= exclusion distance ordered relation which unit
-exclusion ::= '1' | '0' | 'void'
-distance ::= <number>
-ordered ::= '1' | '0'
-relation ::= <number>
-which ::= 'known' | 'private'
-unit ::= <number>
+ query ::= ['@attrset' <attribute-set>] rpn
+ rpn ::= complex | simple | attr rpn
+ complex ::= operator rpn rpn
+ operator ::= '@and' | '@or' | '@not' | '@prox' proximity
+ simple ::= term | set.
+ term ::= <word> | '"' <term> ... '"'.
+ set ::= '@set' <setname>.
+ attr ::= '@attr' [<attribute-set>] <number> '=' <number>.
+ proximity ::= exclusion distance ordered relation which unit
+ exclusion ::= '1' | '0' | 'void'
+ distance ::= <number>
+ ordered ::= '1' | '0'
+ relation ::= <number>
+ which ::= 'known' | 'private'
+ unit ::= <number>