Exceptions to code set knowledge: unique code-point range

Because of the way the supported code sets are organized, there is one exception to the statement: "No knowledge of the underlying code set can be assumed in a program."

When a multibyte character string is searched for any character within the unique code-point range (for example, the . (period) character), it is not necessary to convert the string to process code form. It is sufficient to just look for that character (.) by examining each byte. This exception enables the kernel and utilities to search for the special characters . and / while parsing file names. If a program searches for any of the characters in the unique code-point range, the standard string functions that operate on bytes (such as the strchr subroutine), should be used. For a list of the characters in the unique code-point range, see ASCII characters.