3.6.1 Canonicalization and Text Defaults

Internet media types are registered with a canonical form. In general, an Entity-Body transferred via HTTP must be represented in the appropriate canonical form prior to its transmission. If the body has been encoded with a Content-Encoding, the underlying data should be in canonical form prior to being encoded.

Media subtypes of the "text" type use CRLF as the text line break when in canonical form. However, HTTP allows the transport of text media with plain CR or LF alone representing a line break when used consistently within the Entity-Body. HTTP applications must accept CRLF, bare CR, and bare LF as being representative of a line break in text media received via HTTP.

In addition, if the text media is represented in a character set that does not use octets 13 and 10 for CR and LF respectively, as is the case for some multi-byte character sets, HTTP allows the use of whatever octet sequences are defined by that character set to represent the equivalent of CR and LF for line breaks. This flexibility regarding line breaks applies only to text media in the Entity-Body; a bare CR or LF should not be substituted for CRLF within any of the HTTP control structures (such as header fields and multipart boundaries).

The "charset" parameter is used with some media types to define the character set (Section 3.4) of the data. When no explicit charset parameter is provided by the sender, media subtypes of the "text" type are defined to have a default charset value of "ISO-8859-1" when received via HTTP. Data in character sets other than "ISO-8859-1" or its subsets must be labelled with an appropriate charset value in order to be consistently interpreted by the recipient.

Note: Many current HTTP servers provide data using charsets other than "ISO-8859-1" without proper labelling. This situation reduces interoperability and is not recommended. To compensate for this, some HTTP user agents provide a configuration option to allow the user to change the default interpretation of the media type character set when no charset parameter is given.