“Event delegation has become increasingly important as size and
complexity of pages grow. Application frameworks such as Backbone
and Sproutcore make heavy use of event delegation. With that in
mind, jQuery 1.7 event handling was refactored with an eye to
making delegated events much faster, especially for the most common
cases.To optimize the code for the most commonly used forms of
selectors, we examined a cross-section of code from Google
Codesearch. Nearly two-thirds of the selectors used in .live() and
.delegate() method calls were in the form tag#id.class where one or
more of tag, id, or class were used.