QGIS PDOK Locatieserver Locator Filter Plugin
This is a so called QgsLocator filter, implemented as a QGIS plugin.
Read about writing one here:
This Locator Filter searches for names in the dutch national search service PDOK
You can install this 'Locator Filter' as a plugin by searching for it in the QGIS plugin manager in your QGIS desktop, search for 'pdok':
Some more docs and api's: