The ol/source/DFCI display the
French DFCI grid.
It can display the 100 x 100 km, the 20 x 20 km, the 2 x 2 km grids and the 5 subdivisions of the 2km.
The data can be loaded on data.gouv.fr (7.3Mo zip), but why loading data you can calculate on the fly?
The ol/control/SearchDFCI is a search tool to find the position of a DFCI grid index.
Conevenient function can be used to handle DFCI indexes: