$$ Condition ::= Comparison ({"and" Comparison} | {"or" Comparison}) . $$ Comparison ::= ["not"] (Expression [Comparison-Operator Expression] | Match-Comparison) . $$ Comparison-Operator ::= "=" | "/=" | "~" | "/~" | "in" | "less" | "greater" | "less_equal" | "greater_equal" .
A condition can either be true or false, as in ``Verb = Verb'' or `` Verb = Noun'', respectively. An expression that is evaluated to any of the symbols yes or no is a valid condition.
A condition can be used everywhere a (non-constant) value is needed. It will evaluate to yes or no. In this case, the condition must be surrounded by parentheses.