I was looking at SLD 1.0 today and ran into this:
> The default if neither an ExternalGraphic nor a Mark is specified is
> to use the default
> mark of a “square” with a 50%-gray fill and a black outline, with a
> size of 6 pixels,
> unless an explicit Size is specified. This definition allows a
> reasonable display to be
> selected very simply.
I recently had to mess around with uDig because this default 6x6 square
had grown to 16x16?
If I read a bit further I find that for ExternalGraphic:
> The default size of an image format (such as GIF) is the inherent size
> of the image. The
> default size of a format without an inherent size (such as SVG) is
> defined to be 16 pixels
> in height and the corresponding aspect in width.
So we have two clear indications of a default size; and no clear
indication for the size of a default Mark.