In Alexander Gessler’s FBX Binary Specification for Blender (obtained, as I understand it, by reverse engineering), it is written:
Bytes 21 - 22: [0x1A, 0x00] (unknown but all observed files show these bytes).
I understand that [0x1A, 0x00] is simply the header size in hexadecimal, little-endian order (26 bytes).
What do you think? After confirmation or consensus, what about a minor update of the documentation?