Compositions are collections of Parts that share common global settings and configuration. Any time you save your work, or later load it again, you are saving or loading a Composition.
The graphic above represents the data that is embedded in a Composition.
Note that some data may or may not be present in any given Composition file! For example, Tempo settings are not saved with Compositions created in the AUv3 version of Mass. This will not affect your ability to load that Composition in the standalone version of Mass later.
A Composition can contain up to 16 Parts at any time. Each Part that is created is given a numerical ID, which is unique and will not be reused later. When you create a new Part, the ID it receives is previous ID + 1. This is true even if the previous Part was deleted. For example, let's say your most-recent Part has an ID of 4. If you decide to delete that Part for any reason, the next Part you create will still have an ID of 5.
Note that Part IDs are presented in the UI largely for relational purposes, and in general are considered internal data.
For detailed information about Parts, and the data they contain, see Parts.
One of the primary Composition-level controls at your disposal is the Pitch Quantizer. This suite of settings allows you to constrain all MIDI notes generated by your Events to a common key. All Pitch Quantizer values are saved with your Composition.
For detailed information about the quantization options, see Pitch Quantizer.
Compositions in the standalone version of Mass save the current working tempo, even if it is derived from an external clock. This allows you to work with an external clock source, and later pick up with the same Composition in a different gear configuration without having to remember the tempo you were working at.
Note: the Composition does not save the clock or transport source settings.
For detailed information about the clock options, see Clock.
Utilize the Composition Browser to save and load Compositions, including creating subdirectories for organizing your workflow.
For detailed information about the browser, see Composition Browser.