This web page responds to gesture events only, so make sure to view this on a device with a multitouch display.
"Pinching" a paragraph will increase and decrease its font size. Rotating two fingers on a paragraph will change its opacity (think of it like turning an "opacity knob").
Note how rotation and scaling may change simultaneously. Thus, in practice it is typically less confusing for the user if a gesture-capable web page sets up its event handlers so that changes are made according to just scaling or just rotation.