What SVG features does Inkscape implement?
The main parts of SVG that Inkscape does not support yet are some of the filters (most are supported as of 0.46), animation (work on it is in planning stages) and SVG fonts (implementation work is under way). The rest mostly works, though of course there are bugs that we’re always fixing. For a comparison of Inkscape and other open source SVG tools on the W3C SVG test suite, look here.