The coordinates are counted from the lower left corner and beginning with 0.
The default values are 0.
If both this coordinates and the size parameters <W>, <H> are missing,
then the modifier acts on the whole area of the picture
with the exception of the [ANIM: ],
[WIN: ] modifiers and the similar <SourceX>, <SourceY> parameters
of the families of the [A: ] and [WO: ] modifiers,
which are dealing with several small pictures copied together into a single picture -
the default values are determined by the number of the pictures, or by the size of the target area.