The third major design goal for the normalization forms is efficiency. This goal is highly desired, but not required. It is possible to implement the Normalization Forms in an efficient manner. In particular, it should be possible to produce Normalization Form C quickly from strings that are in either Normalization Form D or C. Versioning Because additional composite characters may be added to future versions of the Unicode standard, composition is less stable than decomposition. Therefore, it is necessary to specify a fixed version for the composition process, so that implementations can get the same result for normalization even if they upgrade to a new version of Unicode.
Decomposition is only instable if an existing character decomposition mapping changes.
The Unicode Technical Committee has the policy of carefully reviewing proposed corrections in character decompositions, and only making changes where the benefits very clearly outweigh the drawbacks. The fixed version of the composition process is defined by reference to a particular version of the Unicode Character Database. For example, suppose that Unicode version 3.0 adds the composite H-caron . However, there are circumstances with possible ambiguities, which requires the precise specification in this document. Normalization Form CC does not attempt to map characters to compatibility composites.