SVG is a markup language for describing two-dimensional graphics applications and images, and a set of related graphics script interfaces.

That is probably one of the “understatements of the century” kind of things. At least, it would appear that way to folks like myself who have never worked with such things (nor had the need to hand-code Postscript as seemingly many others have).
The fact that full access to the document is provided for the HTML container and is entirely accessible both to and from JavaScript makes this a quite amazing computational/visual platform.

Realtime web development with skewer and Emacs

[skewer-mode] provides live interaction with JavaScript, CSS, and HTML in a web browser. Expressions are sent on-the-fly from an editing buffer to be evaluated in the browser, just like Emacs does with an inferior Lisp process in Lisp modes.

Looks like a pretty nice option if you are used to Emacs already and so much more pleasant then running code in the Chrome/Firefox/IE REPL.