# Selecting Parts of Meshes (DMLabel)

The `DMLABEL` object is used to mark pieces of a mesh or `DM`, for example to indicate that a boundary condition should hold on that section.
Markers are integers, so it can be seen as a multimap between integers and mesh pieces.

Insertion is amortized $O(1)$ since hash tables are used,
but each bin is then sorted so that extraction into sorted levels is also $O(1)$. The total cost should be $O(N log N)$ for $N$ entries.