The SVG content document definition has this requirement:

The [svg] title element MUST contain only valid XHTML content document Phrasing content.

The link just redirects back to the general xhtml requirements, however; there are no references to phrasing content.

I assume this is supposed to mean HTML phrasing content that conforms to the XHTML content document restrictions, but it's not clear at all from the description.

It also makes it sound like you have to have an xhtml namespaced element even if the title is text only. I know the phrasing content definition includes text, but the description makes it sound like all content needs to be in the xhtml namespace.

Could we perhaps rewrite this more simply like:

The [svg] title element MAY contain [[html]] phrasing content that conforms to 6.1.4 XHTML requirements. It MUST NOT contain elements from other namespaces.