Where does the resize handle on browser textboxes come from? Is it a browser* implementation, or an HTML/CSS/JavaScript/etc. implementation?
Is it standardized across browsers/operating systems/frameworks/protocols/etc. in any way?
I notice that it's sometimes missing from textboxes -- like Superuser's question textbox -- which leads me to believe there's some sort of HTML/CSS interaction factoring into play.
But maybe not.
*(For reference, I'm using Firefox v22 on Windows 7 x64)