As section 1.3
SVG Namespace, Public Identifier and System Identifier of the specification says: «While a DTD is provided in this specification, the use of DTDs for validating XML documents is known to be problematic.
Not exact matches
-- proprietary extension of CSS Media Queries — proprietary xml
namespace — «contains a weird where the target is really a
SVG document.
As noted, I needed to to add a
namespace for XLINK to my
SVG file.