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4.4 rfc2047

RFC2047 (Message Header Extensions for Non-ASCII Text) specifies how non-ASCII text in headers are to be encoded. This is actually rather complicated, so a number of variables are necessary to tweak what this library does.

The following variables are tweakable:

rfc2047-header-encoding-alist
This is an alist of header / encoding-type pairs. Its main purpose is to prevent encoding of certain headers.

The keys can either be header regexps, or t.

The values can be nil, in which case the header(s) in question won't be encoded, mime, which means that they will be encoded, or address-mime, which means the header(s) will be encoded carefully assuming they contain addresses.

rfc2047-charset-encoding-alist
RFC2047 specifies two forms of encoding—Q (a Quoted-Printable-like encoding) and B (base64). This alist specifies which charset should use which encoding.
rfc2047-encode-function-alist
This is an alist of encoding / function pairs. The encodings are Q, B and nil.
rfc2047-encoded-word-regexp
When decoding words, this library looks for matches to this regexp.
rfc2047-encoded-word-regexp-loose
This is a version from which the regexp for the Q encoding pattern of rfc2047-encoded-word-regexp is made loose.
rfc2047-encode-encoded-words
The boolean variable specifies whether encoded words (e.g., ‘=?us-ascii?q?hello?=’) should be encoded again. rfc2047-encoded-word-regexp is used to look for such words.
rfc2047-allow-irregular-q-encoded-words
The boolean variable specifies whether irregular Q encoded words (e.g., ‘=?us-ascii?q?hello??=’) should be decoded. If it is non-nil, rfc2047-encoded-word-regexp-loose is used instead of rfc2047-encoded-word-regexp to look for encoded words.

Those were the variables, and these are this functions:

rfc2047-narrow-to-field
Narrow the buffer to the header on the current line.
rfc2047-encode-message-header
Should be called narrowed to the header of a message. Encodes according to rfc2047-header-encoding-alist.
rfc2047-encode-region
Encodes all encodable words in the region specified.
rfc2047-encode-string
Encode a string and return the results.
rfc2047-decode-region
Decode the encoded words in the region.
rfc2047-decode-string
Decode a string and return the results.
rfc2047-encode-parameter
Encode a parameter in the RFC2047-like style. This is a substitution for the rfc2231-encode-string function, that is the standard but many mailers don't support it. See rfc2231.