ProDOS / Autostart ROM ID bytes

["vladitx" <vladitx@nucleusys.com>]

Hello,

Trying to understand Alex Freed's PD8, I found this at the beginning of
the boot firmware code:

;; $Cx00
        ldx     #$20    ; ID bytes for ProDOS and the
        lda     #$00    ; Apple Autostart ROM
        cpx     #$03    ;
        cpx     #$3C    ; this one for older II's

Does someone remember the exact and full requirements to be:
  - recognized by Autostart ROM on ][+, //e, //c, etc.
  - recognized by ProDOS as a block device driver

Regarding ProDOS driver structure, is there public document describing
all requirements like entry points, etc.? Example source template will
be appreciated.