Some characters can be represented directly as single ASCII bytes. The first group is known as "direct characters" and contains 62 alphanumeric characters and 9 symbols: codice_1. The direct characters are safe to include literally. The other main group, known as "optional direct characters", contains all other printable characters in the range –U+007E except codice_2 and space (the characters and being excluded due to being redefined in "variants of ASCII" such as JIS-Roman). Using the optional direct characters reduces size and enhances human readability but also increases the chance of breakage by things like badly designed mail gateways and may require extra escaping when used in encoded words for header fields.