Library is a global MultiLevelIdentityDictionary. The Library can be used as a place to store data that you want globally accessible. It is an alternative to using class variables. It is a nice place to store menus, annotations, and commonly reusable functions.
Post a formatted description of the entire library.
The last argument to put is the object being inserted:
Library.put(\multi, \level, \addressing, \system, "i'm the thing you are putting in here"); Library.at(\multi, \level, \addressing, \system).postln; Library.atList([\multi, \level, \addressing, \system]).postln;