The Unicode Character Encoding Stability Policies ensure that developers know what they can depend on between successive releases of the Unicode Standard.
Recent changes to these policies include new guarantees:
Property aliases will not be reused later for different properties.
Property value aliases will not be reused later for different property values.
Characters with the General_Category of Number are guaranteed to have a corresponding Numeric_Type value.
Additionally, the wording for two earlier guarantees about General_Category and Bidi_Class have been clarified:
No new General_Category property values will ever be added.
New Bidi_Class property values can only be added for a tightly constrained class of new character additions.
For the exact wording of these new and updated guarantees, see Unicode Character Encoding Stability Policies. http://www.unicode.org/policies/stability_policy.html