Alright, I\'ve search the jQuery docs (needs somebody devoted to maintaining), I\'ve searched SO, and I\'ve searched Google. I can\'t find the answer to this question.
jQuery now uses a cssHooks feature for certain .css() requests, width and height in particular.
cssHooks
.css()
width
height
So the width() function and the .css('width') both run through the same code on occasion.
width()
.css('width')