New line numbering plugin that uses ::before rather than a new element

I created a line numbering plugin that's much shorter and that doesn't create a new element to put the line numbers in; it wraps each line with a <span class=line> and uses CSS ::before to create the line numbers.
(As written, lines start by default with 0 rather than 1; that's my quirk. Easily changed).
Examples on my blog: http://bililite.com/blog/2013/09/03/fun-with-before-and-after/