Hello,
TAGS meaning:
<M ....> 2d marker definition (i index, x, y)
<MTL ....> Material definition (i index, n name)
<MG ...> Material group, (m=material index, f=indexes of faces of the group)
I suggest to ask support@realviz.com for more detqilled information on RZML (Realviz XML).
Best,
Stef