The expression evaluator allows powerful filters and modifications.

There are four data types, just like UDAs:

    string             project, description
    date               due, wait ...
    duration           recur
    numeric            urgency

There are several forms of literals:

    rc.name            configuration
    <dom>              task-specific data
    <numeric>          numbers
    <date>             either ISO-8601 or rc.dateformat dates
    <duration>         either ISO-8601 or durations

There are many supported operators:

    +                  addition, concatenation
    -                  subtraction, unary minus
    *                  multiplication
    /                  division
    ( )                precedence
    and or xor not !  logical operators
    < <= > >=          relation operators
    = !=               equality operators
    ~ !~               match operators

There are helper operators to perform odd operations:

    __hastag__         presence of a tag
    __notag__          absence of a tag

