[brechtm]

RinohType [1] combines a CSS-inspired style sheet system [2] with a powerful layout system based on boxes ("containers"). It currently only outputs to PDF but an SVG backend could be added without too much work...

[1] http://www.opqode.com [2] http://www.mos6581.org/rinohtype_status_update_1

(I'm RinohType's author)