M2/.skel

chunks are probably seq, bone, attach

SKL1

struct skl1chunk {
  int a;
  int lenname;
  int c;
  int d;
  char name[lenname];
  char e[size-16-b];
} skl1;

SKPD

uint8_t _0x00[8];
uint32_t parent_skel_file_id;
uint8_t _0x0c[4];

The parent skeleton file data id is used for de-duplication. E.g. lightforgeddraeneimale references draeneimale_hd. lightforgeddraeneimale does not have any M2/.anim files, but uses those of draeneimale_hd via parent-link (does not even have an AFID chunk).

AFID

anim file ids, somehow duplicated from .m2

BFID

bone file ids, somehow duplicated from .m2