returns: above example returns a collection of all P elements inside the first form matching ALL criteria,
including elements with class="class1 class2 class3",
but not elements with just class="class1"
drawbacks: slightly different way to invoke: straight function call with 3 parameters
(last 2 optional), instead of DOM method with 1 parameter
- so that could contribute to a little bit of confusion
note: this does not redefine DOM method, which could still be invoked