Editing Base64 (section)

===UTF-7===
{{Main|UTF-7}}
[[UTF-7]], described first in {{IETF RFC|1642}}, which was later superseded by {{IETF RFC|2152}}, introduced a system called ''modified Base64''. This data encoding scheme is used to encode [[UTF-16]] as [[ASCII]] characters for use in 7-bit transports such as [[SMTP]]. It is a variant of the Base64 encoding used in MIME.<ref>{{cite IETF |title=UTF-7 A Mail-Safe Transformation Format of Unicode |rfc=1642 |date=July 1994 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=March 18, 2010}}</ref><ref>{{cite IETF |title=UTF-7 A Mail-Safe Transformation Format of Unicode |rfc=2152 |date=May 1997 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=March 18, 2010}}</ref>

The "Modified Base64" alphabet consists of the MIME Base64 alphabet, but does not use the "<code>=</code>" padding character. UTF-7 is intended for use in mail headers (defined in {{IETF RFC|2047}}), and the "<code>=</code>" character is reserved in that context as the escape character for "quoted-printable" encoding. Modified Base64 simply omits the padding and ends immediately after the last Base64 digit containing useful bits leaving up to three unused bits in the last Base64 digit.