The basic structure of a condition is:

Operand Operator Operand

Operands include constants, variables, attributes and data type-specific functions.

If a user-defined function has a return value and it is either real64 or int32, the function can be used directly as an operand.

All user-defined functions without a return value or with text or tuples as return values cannot be used as operands.

isValid is also a valid condition. The call does not match the pattern Operand Operator Operand. This is the only exception.