All Functions begin with the @ character.
Day Of Month - @DOM(Date String)
Day Of Week - @DOW(Date String)
Date - @DATE(Current Date)
DateVal - @DATEVAL(Numeric Date)
Date Text - @DATETEXT(Numeric Date)
Format - @FORMAT(Expression, FormatString)
If-Then-Else - @IF(Expression,TruePart,FalsePart)
Left Characters - @LEFT(Text,NumCharacters)
Middle Characters - @MID(Text,NumCharacters1,NumCharacters2)
Middle Characters (to end) - @MID(Text,NumCharacters)
Not Equal To - @NOT(Expression)
Right Characters - @RIGHT(Text,NumCharacters)
Wrap (number of characters) - @WRAP (Text,NumCharacters1,NumCharacters2)
Wrap (width only) - @WRAP (Text,Width)
See:
Edit Variable Screen
Variables in SubTotals and Grand Totals
Filters and Formula Operators
Filters - Transaction Types