Mapping API with multiple return values

[msx80]

Hi there, i was looking at the c64 kernal functions, i saw something like this:

// SAVE. Save file. (Must call SETLFS and SETNAM beforehands.)
// Input: A = Address of zero page register holding start address of memory area to save; X/Y = End address of memory area plus 1.
// Output: Carry: 0 = No errors, 1 = Error; A = KERNAL error code (if Carry = 1).
asm clear_carry save(byte register(a) address, word register(xy) past_end) @$FFD8 extern

Now the function returns two things: an error indicator in Carry and an error code in A. How should i use it? There's nothing on the call signature that tells that A will return something, so i just have to know it? If so, how do i capture it?

Thanks.