HTTP allows clients to express preferences for the language and encoding of documents which servers may honor. For each of these variables, the value is a string; it can specify a single choice, or it can be a comma-separated list.
Normally, this list is ordered by descending preference. However, each
element can be followed by ‘;q=priority’ to specify its
preference level, a decimal number from 0 to 1; e.g., for
"de, en-gb;q=0.8, en;q=0.7". An element that has no ‘;q’ specification has
preference level 1.
HTTP allows specifying a series of MIME charsets which indicate your preferred character set encodings, e.g., Latin-9 or Big5, and these can be weighted. The default series is generated automatically from the associated MIME types of all defined coding systems, sorted by the coding system priority specified in Emacs. See Recognizing Coding Systems.