ISSUE: SVG 1.2 attribute name conflict in 11.9

Hi all,

    There is an important attribute name conflict in 11.9
"Filter Region extensions".

    This adds the attributes 'dx', 'dy', 'dw', 'dh' to all
filter primitives, but feOffset already has 'dx', 'dy'.
I would suggest renaming the new attributes:

    'extendX', 'extendY', 'extendW', 'extendH' - or -
    'mx', 'my', 'mw', 'mh' (m = margin)

    Also I was wondering if the WG would consider having
these attributes 'override' x/y/width/height.  So if
'mx' is set 'x' goes to '0' in objectBoundingBox.

    Otherwise, someone needs to set at least _eight_
attributes to correctly use the new feature.  You
might also consider adding a new filterRegionUnits
value of 'none' which would cause the old filter region
values to be ignored (then you only need to set 5 :/).