The source code character set is the set of characters allowed for writing source code programs. The execution character set is the set of characters recognized and used by running programs. The source code character set can vary for different parts of the language. Very few programming languages require a specific character encoding for the execution character set. A common cross-platform programming error is to assume a specific character set.
Some programming languages define additional characters as white space.
These may include horizontal tab, vertical tab, end of line, form feed, carriage return, and line feed. In some programming languages, comments are treated as white space. White space is sometimes compacted into a single space character by the compiler. Fixed line lengths typically occur with programming languages that use columns. Some programming languages have special character sequences for encoding required characters on older hardware that doesn't support all of the required source code character set.