<altGlyph> element not implemented
One way to implement this would be to pre-flight any SVG text we're about to render, manually replacing
glyphs in the RenderText with the equivilent of a <tspan>. Not sure. This one is going to need some
*** Bug 6482 has been marked as a duplicate of this bug. ***
This is the last element blocking our enabling of the "Text" feature string for SVG 1.1.
This has been implemented in 2008 already! Closing.