The declare keyword forward-declares a subroutine or function.

DECLARE SUB <name> ([arg1 AS <type> [, arg2 AS <type>, ... ]]) [OVERRIDE] [STATIC] [SHARED]
DECLARE FUNCTION <name> AS <type> ([arg1 AS <type> [, arg2 AS <type>, ... ]]) [OVERRIDE] [STATIC] [SHARED]

Read more about forward declaration here.

• FUNCTION
• SUB