Note:

• The example demostrate dependent dropdown, or sometimes called nested dropdown. It can be nested in unlimited level.
• It's important that all the dropdowns must be set to "autocomplete" edit type before calling set_nested_dropdown() method.
• Due to the way the select is implemented in jqGrid, the 3rd parameter of set_col_edittype() method must contain the
  ENTIRE string of all the key:value pair of that column, or the data will appear to be missing when display. There is no way around due to the jqGrid limitation.
• The dependency logic is essentially embedded in the javascript data source (e.g. $countryStateData) used to populate the dropdown dynamically based on
  its selected parent value.
• Nested dropdown only works in INLINE edit at the moment.