$bodygroup
Template:Otherlang2 $bodygroup is a QC command that defines a group of meshes that can be turned on or off. Server code can change their state.

Example
$bodygroup sights
{
studio "ironsights.smd"
studio "laser_dot.smd"
blank
}
This bodygroup allows a weapon to have iron sights, laser sights, or no sights at all.
$bodygroup chest
{
studio "chest_with_no_armor.smd"
studio "chest_with_light_armor.smd"
studio "chest_with_heavy_armor.smd"
studio "chest_with_super_armor.smd"
}
This bodygroup defines the entire chest region of the model, which probably spans multiple bones.

Programming
To change a body group's state:
static int BodyGroup_Sights = FindBodygroupByName("sights"); // calculate this value once
SetBodygroup( BodyGroup_Sights , 1 ); // laser dot
By default, CBaseAnimating
supports 4,294,967,296 combinations (32 bits), and CBaseViewModel
supports 256 (8 bits). You can raise either of these by editing the relevant SendProp for m_nBody
.
To calculate how many combinations you need, multiply the size of all your bodygroups together. The examples on this page total 3 * 4 = 12...but add two more groups the same size and you're up at 144. The figure grows exponentially.