You're right, here's the intro of one the ASM files for my CP/M S-100 computer, it's straight from my WordStar archives. The bare-bones, skeletal outline files came from the board manufacturer but it was constantly tweaked and recompiled using WordStar. The file is 107k bytes long (all preliminaries incl. revs deleted):

WordStar used as editor here:

  "<...>
  ; ========================== Copyright 1983, CompuPro Corporation.
  ; ||     HMX1BIOS.ASM ||
  ; ==========================
  ; CONSTANTS:
  VERS EQU 22 
  ; CP/M version number
  CBIOSV EQU 'N' ;CBIOS revision level (2.2x) (CompuPro level)
  ; LIBRARY CONSTANTS:
      MACLIB  COMPUPRO ;Disk and Serial/Parallel interface constants
      MACLIB  ASCII ;Mnemonics for common ASCII, other special characters
      MACLIB  ACTIVE ;Flags directing construction for the various
  ;CompuPro products to "customize" the BIOS
    MACLIB  CPMDISK ;CP/M disk defaults, CBIOS offsets, BDOS functions
    MACLIB  BOOTSCPM ;CP/M cold/warm boot routines for each of the
  ;possible controller types
  ; PROGRAM:
  ; The next statement produces a harmless error message if MAC is used instead.
      ASEG  ;Used Digital Research RMAC assembler and
   ORG BIOS ;LINK linker to assemble this code
   JMP CBOOT ;+00h Cold boot
  <...>"

Oh for the days when we could actually compile our own BIOSes to suit our needs!