Changesets are typically treated as an atomic unit, an indivisible set, by version control systems.
[9] Unique identifiers are an important part of the metadata which version control systems attach to changesets.
Centralized version control systems, such as Subversion and CVS simply use incrementing numbers as identifiers.
[10][11] Distributed version control systems, such as Git, generate a unique identifier by applying a cryptographic hash function to the changeset.
Changeset content should involve only one task or fix, and contain only code which works and does not knowingly break existing functionality.