(This seems to be related to #173 (comment), although not to rdf:RDF, which is the original topic of that issue.)

The W3C SVG Logo is not accepted by epubcheck, complaining about "External DTD entities are not allowed.". That is problematic.

The SVG file itself does not include any external DTD entity. However, the Logo file does contain:

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">

Indeed, the DTD file itself contains loads of entities. It is also correct that the latest version of SVG (SVG2) has removed the reference to a DTD (see change section). But flagging this is as an error does create backward incompatibility issues with bona fide SVG1.1 content which did rely on the DTD (e.g., all examples in SVG1.1 include that DTD reference, but also all SVG content produced by earlier versions of Adobe Illustrator, to take just this example). Note that all browsers accept such SVG 1.1 content without further ado.

I would think that epubcheck should simply ignore the SVG DTD and shouldn't report any error or warning on that one.