title: Center (proportional font) text in an HTML5 canvas
body: <p>I would like to be able to center single lines of text within rectangular areas I can calculate. The one thing I have expected to do in 2D geometry on a canvas is to center something whose width is unknown to you.</p>
  <p>I have heard as a workaround that you can create the text in an HTML container and then call jQuery's <code>width()</code> function, but I ?didn't correctly handle the momentary addition to the document's body? and got a width of 0.</p>
  <p>If I have a single line of text, significantly shorter than would fill most of the width in a screen, how can I tell how wide it will be on a canvas at a font size I know?</p>