Ext.util.Grouper

The property to sort by. Required unless sorter is provided

Optional root property. This is mostly useful when sorting a Store, in which case we set the root to 'data' to make the filter pull the property out of the data object of each item

A specific sorter function to execute. Can be passed instead of property

A function that will be run on each value before it is compared in the sorter. The function will receive a single argument, the value.