Sections -- section bridgetype_piecetype_pieceposition (IE warren_undertruss_start) (piece definitions) end
piece <instance, rotation> Simple piece piece <instance, rotation, htdelta, yoffset> Sloped piece with the given height change over the tile and model Y offset piece <instance, rotation>:depth Simple piece with support column (: syntax also works for long form) piece section-name Reference a section
Bridge Blocks --
length 5 piece definedsectionfromabove piece repsofpiece*definedsectionfromabove piece rev(definedsectionfromabove) end
Basically a bridge block defines the length of the bridge you are creating the format for, and then defines each of the pieces in that length from one side to the other consecutively followed by an end marker.