Default render image size. The server constrains reply images to be no larger than this width and height, if the request does not specify the view size explicitly using wid= or hei=.
Two integer numbers, 0 or larger, separated by a comma. Width and height in pixels. Either or both values may be set to 0 to keep them unconstrained.
Not applicable to nested/embedded requests.
default::DefaultPix if not defined or if empty.