Test the value of a particular thing and put it in a variable.
Failed tests will result in the specified result variable being cleared.
File tests: directories always have 0 size and their modification time is the time a file was last added or deleted from them. File type is either file or dir.
Contact lookups: based on the phone number of the contact.
Calendar values: require the time in seconds since the epoch as data (e.g. use %TIMES, or use the Variable Convert action to convert a date/time into seconds first) and are entered in an array (%var1, %var2 etc), not a plain value, because there may be multiple events at the time specified.
Variables section in the Userguide.