This will probably progress through the two or three stages:

• The use of a symbol font, here in msym ,
  
  
• The use of images (that can be stretched in various ways), here in jpegs
  
  
• A bit of both here.
  
  
• Aside, a bit of XML/CSS too, just because it's sort of amusing.
  
  
• Beginning to pull it together now in beta.

• html/css works better (on more browsers) than xml/css.
• svg doesn't do transparent - can't use it for beams.