Function of ! $ in tile filenames?

Hi,

A lot of character tiles use either !, $ or a combination in the filename. What is the function of this?

$ means its a character sheet that only has 1 character in it (or in other terms only has 1 3x4 frame) as opposed to the normal sheet which has 8 characters

! means that the sprite will start at the bottom of the tile when drawn. Normal sprites (i.e. those without !) are drawn a few pixels above the bottom of the tile to make them look like they are "on the tile". This is why most ! spritesheets are doors.

Thanks!:)