https://sourceforge.net/tracker/?func=detail&aid=3101986&group_id=152762&atid=785194

Currently, onPaging is used internally for grid, listbox and tree.
User should not listen it.

In some scenario, user may edit data in a page,
and programmer wish to do some check before user go to next page.
For example, if user go to next page without save data first,
programmer would like to have a confirm dialog, and cancel user's action to next page.