The multipatch folder contains all the code describing methods and classes which are specific to a multipatch geometry. It is broken up into the following sub-folders:

Multipatch connectivity - Defines structures and methods to describe patches and how they are connected to one another.
Data Types for Multipatch Geometry - Defines classes to handle objects on a multipatch domain more conveniently.
src_multipatch_interface_derivatives - Ongoing work only available on GitLab.
Spline on multipatch geometry - Defines structures and methods to deal with different splines on every patches.
Multipatch utilitary functions - Defines utility functions to operate over multiple patches.