efficiently watch for changes to a dom element (or its descendents).
$watch observes property modifications on the
$scope, since in angular the
$scope is the source of truth. this is a good pattern for most use cases. however, there are situations where you want modules to be decoupled, and the dom is the fundamental source of truth.
watch custom properties (like what?)
var props =subtree: trueattributeFilter: 'foo' 'bar';watchDom;
ie11+, firefox 28+, chrome 31+, safari 7+, opera 20+, ios 6+, android 4.4+