because I can *not* draw a simple, arbitrary length arrow in JS without coding the actual rendering of the lines pixel by pixel. This is very underwhelming, so say the least!!
If anybody knows differently, please educate me! But JS is just not appropriate for drawing any complex geometrical forms, like a "lab course" at Wikiversity will need.
once I have used a mediawiki extension that allows us to embed svg files in the wikitext inside a <svg></svg> tag. It allows you to dinamically manipulate vectorial elements through javascript, which is enabled inside the svg, even if mediawiki is (as it is by default) blocking javascript on the page. I mean, inside the svg, javascript is always allowed.
This can be used with svg enabled browsers to draw moving arrows, rectangles, elipses, etc. (Firefox 1.5+ supports SVG, and IE needs a plugin for that)
Juca