A fixed property that is also subject to a stability guarantee preventing any change in the published listing of property values other than assignment of new values to formerly unassigned code points.

• An immutable property is trivially stable with respect to all algorithms.
• An example of an immutable property is the Unicode character name itself.

Because character names are values of an immutable property, misspellings and incorrect names will never be corrected clerically. Any errata will be noted in a comment in the character names list and, where needed, an informative character name alias will be provided.

• When an encoded character property representing a code point property is immutable, none of its values can ever change. This follows from the fact that the code points themselves do not change, and the status of the property is unaffected by whether a particular abstract character is encoded at a code point later. An example of such a property is the Pattern_Syntax property; all values of that property are unchangeable for all code points, forever.
• In the more typical case of an immutable property, the values for existing encoded characters cannot change, but when a new character is encoded, the formerly unassigned code point changes from having a default value for the property to having one of its nondefault values. Once that nondefault value is published, it can no longer be changed.