Not researched enough. Stores base state, frames deltas, "custom tracks", "triggers", morph data. .performanceclip has the same magic and sections.
animclip_to_gltf.py script applies base state to a given .model and exports as .gltf. Currently support is poor, and exported pose usually doesn't look correct.
Initial pose. Array of joints' transforms, same order as $\color{#3B2664}{◆}$Anim Clip Joint Hashes. Each transform is 16 bytes, each component is packed into 16-bit value. First are quaternion's XYZW, then position XYZ and last two bytes determine scale multipliers.
After this array, sometimes extra data is present. Seems to be another array, 32 bytes per element. Number of items in array is specified in one of the fields of $\color{#DF23F7}{◆}$Anim Clip Built, but purpose is unknown. 16 bytes halves seem to have the same format.
Array of custom track structs. Each struct is 40 bytes long. Contains 32-bit offset to name in strings block, offset and count for $\color{#16EB68}{◆}$Anim Clip Custom Track Data, and a few other 32-bit values.
$\color{#16EB68}{◆}$ 116EB684: Anim Clip Custom Track Data
Not researched enough. Array of 32-bit values (ascending order), then array of byte values, same size. Number of elements matches some values in $\color{#DF23F7}{◆}$Anim Clip Built or $\color{#4014CB}{◆}$Anim Clip Custom Tracks.
$\color{#A7B485}{◆}$ 3A7B4855: Anim Clip Sample Data