And if you wanted 'and' to be higher precedence than 'or' and 'xor', so as not to confuse the rest of us:

expression: <leftop: term termop term>
termop: 'or' | 'xor'
term: <leftop: factor factorop factor>
factorop: 'and'
factor: '(' expression ')' | condition
condition: field comparison value
field: '<' timethingy '>'
timethingy: 'DAY' | 'WEEK'
comparison: '<=' | '<' | '=' | '>=' | '>' | '!='
value: /\d+/
[download]

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.