Returns the inverse RFC1421 transformation of <stuff>, commonly known as Base64. The inverse transformation converts four Base64 digits into three bytes.
Alas, because ircII only supports C strings, if <stuff> decodes to binary data (with nuls) it will probably not do what you hope.
The reverse transformation is b64encode.
Don't confuse this encoding with the one used by FiSH (popularized by eggdrop and other irc clients for encrypted messages). FiSH uses l64a encoding, and can be decoded using the xform FISH64 transform.
The rfc1421 string <stuff> converted into a C string.