Derive Macro Part 

#[derive(Part)]
{
    // Attributes available to this derive:
    #[part]
}

Derives Part for a vocabulary of mesh parts: each fieldless variant (and a unit struct) is named by what it is called in code, or by #[part("...")] when the loaded material name cannot be written as one — repeat the attribute for other spellings. The variants are numbered in order, which is the position a draw’s override of one is stored at.

A variant with fields fails to compile: a part is a plain name.