Restriction on epub:type in svg is too strict #2556
Description
As reported in w3c/epubcheck#1497, the current restriction on epub:type in svg content documents does not allow the attribute on a elements.
The definition of renderable elements is probably a better alternative than the three categories listed.
(If the current three categories are kept, however, note that they link to the svg 1.1 specification so should be updated.)