"SVG data parsing failed cause the document does not have a root node." error on OpenClipArt files

[Shnatsel]

Many of the files in OpenClipArt library fail to render with resvg with the following message:

Error: SVG data parsing failed cause the document does not have a root node.

They are rendered by librsvg and Inkscape. Tested on commit e3cfe1a

Archive with all files failing with this error message:
no_root_node.tar.gz

[RazrFalcon]

An SVG file must have a xmlns="http://www.w3.org/2000/svg" namespace. Without it, it is malformed. Browsers and Batik will not load such files too. I think that Inkscape and librsvg are incorrect in this regard.

For example, librsvg v2.47.1 doesn't support mixed namespaces. You can test it on e-svg-003.svg