Which of these input semantics can I expect in a <vertices> element and which in a <triangles> element (or other primitive types)? I could not find anything in the spec about this.
BINORMAL
COLOR
CONTINUITY
IMAGE
IN_TANGENT
INPUT
INTERPOLATION
INV_BIND_MATRIX
JOINT
LINEAR_STEPS
MORPH_TARGET
MORPH_WEIGHT
NORMAL
OUTPUT
OUT_TANGENT
POSITION
TANGENT
TEXBINORMAL
TEXCOORD
TEXTANGENT
UV
VERTEX
WEIGHT
If you want to export data that is not describe in these semantic, you can definitely create your own semantic for now. For example, FOGCOORD and FOGCOLOR are not in the lists.
Other importer might not understand these new semantic, but at least you won’t lose data when you import it back in your application.
When we see enough audience on a new semantic, we can try to push it in to the next revision of the COLLADA spec.