HTML as an Internet Media Type

An HTML user agent allows users to interact with resources which have HTML representations. At a minimum, it must allow users to examine and navigate the content of HTML level 1 documents. HTML user agents should be able to preserve all formatting distinctions represented in an HTML document, and be able to simultaneously present resources referred to by IMG elements (they may ignore some formatting distinctions or IMG resources at the request of the user). Level 2 HTML user agents should support form entry and submission.

text/html media type

This specification defines the Internet Media Type[IMEDIA] (formerly referred to as the Content Type[MIME]) called `text/html'. The following is to be registered with [IANA].

Media Type name

text

Media subtype name

html

Required parameters

none

Optional parameters

level, charset

Encoding considerations

any encoding is allowed

Security considerations

see section Security Considerations

The optional parameters are defined as follows:

Level

The level parameter specifies the feature set used in the document. The level is an integer number, implying that any features of same or lower level may be present in the document. Level 1 is all features defined in this specification except those that require the FORM element. Level 2 includes form processing. Level 2 is the default.

Charset

The charset parameter (as defined in section 7.1.1 of RFC 1521[MIME]) may be given to specify the character encoding scheme used to represent the HTML document as a sequence of octets. The default value is outside the scope of this specification; but for example, the default is `US-ASCII' in the context of MIME mail, and `ISO-8859-1' in the context of HTTP [HTTP].

HTML Document Representation

A message entity with a content type of `text/html' represents an HTML document, consisting of a single text entity. The `charset' parameter (whether implicit or explicit) identifies a character encoding scheme. The text entity consists of the characters determined by this character encoding scheme and the octets of the body of the message entity.

Undeclared Markup Error Handling

To facilitate experimentation and interoperability between implementations of various versions of HTML, the installed base of HTML user agents supports a superset of the HTML 2.0 language by reducing it to HTML 2.0: markup in the form of a start-tag or end-tag, whose generic identifier is not declared is mapped to nothing during tokenization. Undeclared attributes are treated similarly. The entire attribute specification of an unknown attribute (i.e., the unknown attribute and its value, if any) should be ignored. On the other hand, references to undeclared entities should be treated as data characters.

For example:

<div class=chapter><h1>foo</h1><p>...</div>
  => <H1>,"foo",</H1>,<P>,"..."
xxx <P ID=z23> yyy
  => "xxx ",<P>," yyy
Let &alpha; &amp; &beta; be finite sets.
  => "Let &alpha; & &beta; be finite sets."

Support for notifying the user of such errors is encouraged.

Information providers are warned that this convention is not binding: unspecified behavior may result, as such markup does not conform to this specification.

Conventional Representation of Newlines

SGML specifies that a text entity is a sequence of records, each beginning with a record start character and ending with a record end character (code positions 10 and 13 respectively) (section 7.6.1, "Record Boundaries" in [SGML]).

[MIME] specifies that a body of type `text/*' is a sequence of lines, each terminated by CRLF, that is, octets 13, 10.

In practice, HTML documents are frequently represented and transmitted using an end of line convention that depends on the conventions of the source of the document; frequently, that representation consists of CR only, LF only, or a CR LF sequence. Hence the decoding of the octets will often result in a text entity with some missing record start and record end characters.

Since there is no ambiguity, HTML user agents are encouraged to infer the missing record start and end characters.

An HTML user agent should treat end of line in any of its variations as a word space in all contexts except preformatted text. Within preformatted text, an HTML user agent should treat any of the three common representations of end-of-line as starting a new line.