the U is the placement along the U [or x] in 0 -1 texture space.

i think what you are after may be in the 2dTextureNode placement options.

look in the docs for other flags for the polyEditUV command other than the defaults the script editor spits put.
unless by align you mean snap?
i dont think align UV is a command, it snaps the UV's to the highes point or lowest point in U or V, this can be done manually. its not a way to clamp the UV to a specific position.
(i.e. U .98 V .34 )