From the site:

This is a simple ActionScript 3 implementation of the class marching ants selection marquee you find in applications such as Photoshop.

The class is based off this ActionScript 2 example here; http://www.nocircleno.com/experiments/selection_ants_proof/index.html, but adds in many more methods and is entirely self contained. Drawing the bitmaps for the marquee internally in the class.

Features:

Either Fixed or user drawn marquee
Draggable or static fixed marque
Programatically changeable marquee colours
Programatically changeable marquee line thickness
Does not rely on library assets for marquee

http://www.blog.noponies.com/archives/80