I have a nice background on my page, and I want my text header to act as a mask to cut through its containing div and have the background as a texture.
Can I
Limited browser support, but background-clip
can get you this effect: http://tympanus.net/Tutorials/ExperimentsBackgroundClipText/ (Hit the Animate buttons for more fun)
Using SVG you can do it like this: http://people.opera.com/dstorey/images/newyorkmaskexample.svg (View source to see what is actually done, see reference article too)
Using a background image and then CSS, you could do this: http://www.netmagazine.com/tutorials/texturise-web-type-css