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Property Value Stability Table

This table shows the property value stability clauses from Character Encoding Stability, organized by property instead of Unicode version.

Property Group Applicable Properties Constraints

Applicable Unicode Versions

Bidi Bidi_Class (bc) No new Bidi_Class property values will be added, except in the case when they are introduced along with newly encoded characters such as bidirectional format controls. 3.0.0+
Bidi_Class (bc),
Bidi_Mirrored (Bidi_M)
The property values for the bidirectional properties Bidi_Class and Bidi_Mirrored preserve canonical equivalence. 4.0.0+
Bidi_Paired_Bracket_Type (bpt) Characters that have a Bidi_Paired_Bracket_Type property value of Open or Close also have the Bidi_Class property value Other_Neutral (ON) and the Bidi_Mirrored property value Yes. 6.3.0+
Case Case_Folding (cf) The Case_Folding property value is limited so that no string when case folded expands to more than 3× in length (measured in code units). 3.0.1+
Lowercase (Lower),
Uppercase (Upper),
Alphabetic (Alpha)
All characters with the Lowercase property and all characters with the Uppercase property have the Alphabetic property. 4.1.0+
General General_Category (gc) The enumeration of General_Category property values is fixed. No new values will be added. 2.1.3+
General_Category (gc) The General_Category property value Control (Cc) is immutable: the set of code points with that value will never change. 1.1.5+
General_Category (gc) The General_Category property value Private_Use (Co) is immutable: the set of code points with that value will never change. 2.0.0+
General_Category (gc) The General_Category property value Surrogate (Cs) is immutable: the set of code points with that value will never change. 2.0.0+
Name (na),
Jamo_Short_Name (JSN)
Once a character is assigned, both its Name and its Jamo_Short_Name will never change. 2.0.0+
Noncharacter_Code_Point (Nchar) The Noncharacter_Code_Point property is an immutable code point property, which means that its property values for all Unicode code points will never change. 3.1.0+
Identifiers ID_Continue (IDC) Once a character is ID_Continue, it must continue to be so in all future versions. 3.0.1+
ID_Start (IDS) If a character is ID_Start then it must also be ID_Continue. 3.0.1+ 
ID_Start (IDS) Once a character is ID_Start, it must continue to be so in all future versions. 3.0.1+ 
XID_Continue (XIDC) Once a character is XID_Continue, it must continue to be so in all future versions. 3.0.1+
XID_Start (XIDS) If a character is XID_Start then it must also be XID_Continue. 3.0.1+
XID_Start (XIDS) Once a character is XID_Start, it must continue to be so in all future versions. 3.0.1+
Pattern_Syntax (Pat_Syn),
Pattern_White_Space (Pat_WS)
The Pattern_Syntax and Pattern_White_Space properties are immutable code point properties, which means that their property values for all Unicode code points will never change. 4.1.0+
Pattern_Syntax (Pat_Syn),
Pattern_White_Space, (Pat_WS), ID_Continue (IDC),
XID_Continue (XIDC)
If a character has the Pattern_Syntax or Pattern_White_Space property, then it cannot have the ID_Continue or XID_Continue property. 4.1.0+
Normalization Canonical_Combining_Class (ccc) The Canonical_Combining_Class property values are limited to the values 0 to 254. 1.1.5+
Canonical_Combining_Class (ccc) Once a character is assigned, its Canonical_Combining_Class will never change. 3.0.0+
Canonical_Combining_Class (ccc),
General_Category (gc)
All characters other than those with General_Category property values Spacing_Mark (Mc) and Nonspacing_Mark (Mn) have the Canonical_Combining_Class property value 0. 1.1.5+
Decomposition_Mapping (dm) Canonical and compatibility mappings (Decomposition_Mapping property values) are always in canonical order, and the resulting recursive decomposition will also be in canonical order. 2.0.0+
Decomposition_Mapping (dm) Canonical mappings (Decomposition_Mapping property values) are always limited either to a single value or to a pair. The second character in the pair cannot itself have a canonical mapping. 3.0.0+
Decomposition_Mapping (dm) Canonical mappings (Decomposition_Mapping property values) are always limited so that no string when normalized to NFC expands to more than 3× in length (measured in code units). 2.0.0+
Decomposition_Mapping (dm) Once a character is assigned, its Decomposition_Mapping will never change. 4.0.0+
Decomposition_Mapping (dm) Canonical mappings (Decomposition_Mapping property values) to a pair of characters are limited such that the first of the pair in the mapping must have ccc=0, except for the Decomposition_Mapping of the following four characters: U+0344, U+0F73, U+0F75, U+0F81. 2.1.0+
Numeric General_Category (gc),
Numeric_Type (nt)
The set of characters having General_Category=Nd will always be the same as the set of characters having Numeric_Type=de. 4.0.0+
General_Category (gc), Numeric_Type (nt) Characters with the property value Numeric_Type=de (Decimal) only occur in contiguous ranges of 10 characters, with ascending numeric values from 0 to 9 (Numeric_Value=0..9). 6.0.0+
General_Category (gc), Numeric_Type (nt) Characters with the General_Category property value Number (Nd | Nl | No) do not have the Numeric_Type value None. 6.2.0+
Numeric_Type (nt) No new assignment of Numeric_Type=di (Digit) will be made to any character. 6.1.0+