Complex sentence: Inside a program or a custom function, control may be conditionally transferred to a statement identified by a line number or explicit label; if the target is 0 (zero) this terminates the program or returns to a function's caller.
Split into simpler sentences: Inside a program or a custom function, control may be conditionally transferred to a statement identified by a line number or explicit label. If the target is 0 (zero) this terminates the program or returns to a function's caller.