Canonical Form
The MIME specification requires that every simple content type define a standard format, called the canonical form. The MIME specification recommends that data be converted to canonical form before the data is encoded or inserted into a message. The specification describes the canonical form of a few media types and outlines a process for registering new types. The Internet Assigned Numbers Authority publishes a list of assigned media types and maintains a repository of the data format descriptions for those types.
For text, the canonical form uses a carriage return (ASCII 13) followed by a line feed (ASCII 10) to indicate a line break. Typically, an application converts text to canonical form before including the text in a message.
For most other content types, the canonical form is identical to the normal format of the file. A good working strategy is to always convert text to canonical form and to assume that other data does not require conversion. We use this strategy in this manual. Be aware, though, that some file formats might have a canonical form different than the normal format of the data.
There is no canonical form for multipart content types. Instead, each part contained in a multipart body must be in canonical form.