The main use of the NodeLocatorService is to determine where the forms association control should start when it is first displayed. In some scenarios, the picker may need to start in the root of the document library of a Share site or start in the folder where the node being edit is located.
NodeLocators are configured using form control parameters. The name of the NodeLocator implementation is provided as the startLocation parameter and the parameters are provided by a startLocationParameters parameter. They should be provided in the form of query string parameters, that is, name=value&name=value.
The configuration for the example node locator is shown as follows.
<field id="my:association">
<control>
<control-param name="startLocation">{namedfolder}</control-param>
<control-param name="startLocationParams">name=Example</control-param>
</control>
</field>
It looks for a folder named Example in the same folder as the node being edited.