From Valve Developer Community
Thumbnails and image scaling.
Pixel scaling, no thumb tags, no align
Thumb tags, default align
Thumb tags, left align
Jump areas (marked with green X's) tell bots that they must jump to reach the higher connected area, and that this area is not usable as a hiding/sniping spot.
Crouch areas (marked with a blue diagonal slash) force bots to crouch when moving through this area.
Thumb tags, right align
Start dragging area at first corner
Thumb tags, center align
Thumb tags, left, center, right align
Gallery tags
Table enclosure
Model Description
Skins