[BODY:HUMANOID_ARMLESS:2WINGS:2EYES:2LUNGS:HEART:GUTS:ORGANS:HUMANOID_JOINTS:THROAT:NECK:SPINE:BRAIN:SKULL:4TOES:BILL:RIBCAGE]
This takes things from the body_default file. This is the basic form of the creature. It has these parts and they're joined together in the manner described in each body part's entry, but they're not made of anything and don't know how to handle damage. You could combine all of these into a single DUCK body if you liked, but then you'd have to make up another body for something else. And since it would probably have the organ and bone parts mentioned above, that means a lot of repetition.
[BODY_DETAIL_PLAN:STANDARD_MATERIALS]
[REMOVE_MATERIAL:HAIR]
[USE_MATERIAL_TEMPLATE:FEATHER:FEATHER_TEMPLATE]
[BODY_DETAIL_PLAN:STANDARD_TISSUES]
[REMOVE_TISSUE:HAIR]
[USE_TISSUE_TEMPLATE:FEATHER:FEATHER_TEMPLATE]
STANDARD_MATERIALS is in b_detail_plan_default and is a big list saying 'add these materials and apply this in-creature name to them'. Hair is on this list and ducks don't have hair, so it gets removed. Then feathers are called in. Note that this does not
replace hair. It only removes one material from the creature's list and adds one material, in two separate commands. Material templates are in the material_template_default file.
STANDARD_TISSUES works almost the same way. In the tissue files themselves (found in tissue_template_default) is a line saying what material the tissue is made of, and the name given there must match the name given when the material was originally called.
[BODY_DETAIL_PLAN:VERTEBRATE_TISSUE_LAYERS:SKIN:FAT:MUSCLE:BONE:CARTILAGE]
[BODY_DETAIL_PLAN:BODY_HAIR_TISSUE_LAYERS:FEATHER]
[BODY_DETAIL_PLAN:EGG_MATERIALS]
The first of these lines tells the game how much of each material goes into which body part. Eyes and organs are made of themselves, so to speak, and limbs are made of skin, fat, muscle, bone, and cartilage, all arranged into layers. The layers used here have to be declared already; the game can't save them up for later. As with anything starting with BODY_DETAIL_PLAN, the details are in b_detail_plan_default.
The second of these lines has a somewhat misleading name, as the template itself takes whatever tissue type you specify and adds it over the top of any qualifying body parts. It's designed for humanoids, which means that legs and toes are included. Just an odd little detail.
The third of these lines is a little different to the other two, as the materials are explicitly defined instead of being defined by the modder.
[SELECT_TISSUE_LAYER:HEART:BY_CATEGORY:HEART]
[PLUS_TISSUE_LAYER:SKIN:BY_CATEGORY:THROAT]
[TL_MAJOR_ARTERIES]
This selects all heart in the heart and all skin in the throat, and adds major arteries to it. PLUS_TISSUE_LAYER (and similar tokens) adds to the current selection. Putting 'select throat skin' after 'select heart' would cause the heart to be dropped from the selection.
[BODY_DETAIL_PLAN:STANDARD_HEAD_POSITIONS]
[BODY_DETAIL_PLAN:HUMANOID_RIBCAGE_POSITIONS]
The first of these lines orders eyes to go at the front, and only that.
The second says which ribs go over which organ.
[USE_MATERIAL_TEMPLATE:SINEW:SINEW_TEMPLATE]
[TENDONS:LOCAL_CREATURE_MAT:SINEW:200]
[LIGAMENTS:LOCAL_CREATURE_MAT:SINEW:200]
[HAS_NERVES]
[USE_MATERIAL_TEMPLATE:BLOOD:BLOOD_TEMPLATE]
[BLOOD:LOCAL_CREATURE_MAT:BLOOD:LIQUID]
[CREATURE_CLASS:GENERAL_POISON]
[GETS_WOUND_INFECTIONS]
[GETS_INFECTIONS_FROM_ROT]
[USE_MATERIAL_TEMPLATE:PUS:PUS_TEMPLATE]
[PUS:LOCAL_CREATURE_MAT:PUS:LIQUID]
This part calls sinew, blood, and pus, and applies them. Tendons, ligaments, blood, and pus are rather abstract at the moment. The code says that the creature has them, but they're all hardcoded things with no particular location. Blood is handled by having tissues bleed a certain amount when torn and by 'major arteries' being assigned to certain tissue layers, pus just kind of appears when infection is present, and tendons and ligaments are just... there.
There are also a couple of on/off style tags here. 'Has nerves' and the two 'gets infections' tag can be placed anywhere in the creature entry.