Superset
Superset - quick reference
An encoding A is a superset of encoding B when every byte sequence valid in B produces the same character in A. Unicode is a superset of ASCII: all 128 ASCII code points map to the same characters in Unicode. Windows-1252 is a superset of ISO-8859-1, adding characters in the 128-159 range that ISO-8859-1 leaves undefined.
Superset relationships matter for migration. Converting ASCII text to UTF-8 requires zero changes - the bytes are identical for codes 0-127. Converting ISO-8859-1 to UTF-8 requires re-encoding because codes 128-255 become multi-byte sequences. Use our encoding comparison to check which positions change between any two encodings, or see the character sets reference for coverage details.
Superset relationships matter for migration. Converting ASCII text to UTF-8 requires zero changes - the bytes are identical for codes 0-127. Converting ISO-8859-1 to UTF-8 requires re-encoding because codes 128-255 become multi-byte sequences. Use our encoding comparison to check which positions change between any two encodings, or see the character sets reference for coverage details.