If ch represents a lower-case character, Tcl_UniCharToUpper returns the corresponding upper-case character. If no upper-case character is defined, it returns the character unchanged.
If ch represents an upper-case character, Tcl_UniCharToLower returns the corresponding lower-case character. If no lower-case character is defined, it returns the character unchanged.
If ch represents a lower-case character, Tcl_UniCharToTitle returns the corresponding title-case character. If no title-case character is defined, it returns the corresponding upper-case character. If no upper-case character is defined, it returns the character unchanged. Title-case is defined for a small number of characters that have a different appearance when they are at the beginning of a capitalized word.
The next three routines convert the case of UTF-8 strings in place in memory:
Tcl_UtfToUpper changes every UTF-8 character in str to upper-case. Because changing the case of a character may change its size, the byte offset of each character in the resulting string may differ from its original location. Tcl_UtfToUpper writes a null byte at the end of the converted string. Tcl_UtfToUpper returns the new length of the string in bytes. This new length is guaranteed to be no longer than the original string length.
Tcl_UtfToLower is the same as Tcl_UtfToUpper except it turns each character in the string into its lower-case equivalent.
Tcl_UtfToTitle is the same as Tcl_UtfToUpper except it turns the first character in the string into its title-case equivalent and all following characters into their lower-case equivalents.