[ Pobierz całość w formacie PDF ]

on invalid documents [p.334] .
Deprecated
A deprecated element or attribute is one that has been outdated by newer
constructs. Deprecated elements are defined in the reference manual in
appropriate locations, but are clearly marked as deprecated. Deprecated
elements may become obsolete in future versions of HTML.
User agents should continue to support deprecated elements for reasons of
backward compatibility.
Definitions of elements and attributes clearly indicate which are deprecated.
This specification includes examples that illustrate how to avoid using
deprecated elements. In most cases these depend on user agent support for
style sheets. In general, authors should use style sheets to achieve stylistic and
formatting effects rather than HTML presentational attributes. HTML
presentational attributes have been deprecated when style sheet alternatives
exist (see, for example, [CSS1] [p.353] ).
Obsolete
An obsolete element or attribute is one for which there is no guarantee of
support by a user agent. Obsolete elements are no longer defined in the
specification, but are listed for historical purposes in the changes section [p.311]
of the reference manual.
24 Dec 1999 18:26 38
Conformance: requirements and recommendations
4.2 SGML
HTML 4 is an SGML application conforming to International Standard ISO 8879 --
Standard Generalized Markup Language SGML (defined in [ISO8879] [p.353] ).
Examples in the text conform to the strict document type definition [p.265] unless
the example in question refers to elements or attributes only defined by the
transitional document type definition [p.279] or frameset document type definition
[p.297] . For the sake of brevity, most of the examples in this specification do not
begin with the document type declaration [p.60] that is mandatory at the beginning of
each HTML document.
DTD fragments in element definitions come from the strict document type
definition [p.265] except for the elements related to frames.
Please consult the section on HTML version information [p.60] for details about
when to use the strict, transitional, or frameset DTD.
Comments appearing in the HTML 4 DTD [p.265] have no normative value; they
are informative only.
User agents must not render SGML processing instructions (e.g., )
or comments. For more information about this and other SGML features that may be
legal in HTML but aren t widely supported by HTML user agents, please consult the
section on SGML features with limited support. [p.337]
4.3 The text/html content type
HTML documents are sent over the Internet as a sequence of bytes accompanied by
encoding information (described in the section on character encodings [p.42] ). The
structure of the transmission, termed a message entity, is defined by [RFC2045]
[p.354] and [RFC2616] [p.354] . A message entity with a content type [p.53] of
"text/html" represents an HTML document.
The content type for HTML documents is defined as follows:
Content type name:
text
Content subtype name:
html
Required parameters:
none
Optional parameters:
charset
Encoding considerations:
any encoding is allowed
Security considerations:
See the notes on security [p.350]
39 24 Dec 1999 18:26
Conformance: requirements and recommendations
The optional parameter "charset" refers to the character encoding [p.42] used to
represent the HTML document as a sequence of bytes. Legal values for this
parameter are defined in the section on character encodings [p.42] . Although this
parameter is optional, we recommend that it always be present.
24 Dec 1999 18:26 40
HTML Document Representation
5 HTML Document Representation
Contents
1. The Document Character Set . . . . . . . . . . . 41
.
2. Character encodings . . . . . . . . . . . . . 42
.
1. Choosing an encoding . . . . . . . . . . . . 42
.
Notes on specific encodings . . . . . . . . . . 43
.
2. Specifying the character encoding . . . . . . . . . 43
.
3. Character references . . . . . . . . . . . . . 45
.
1. Numeric character references . . . . . . . . . . 45
.
2. Character entity references . . . . . . . . . . . 46
.
4. Undisplayable characters . . . . . . . . . . . . 47
.
In this chapter, we discuss how HTML documents are represented on a computer
and over the Internet.
The section on the document character set [p.41] addresses the issue of what
abstract characters may be part of an HTML document. Characters include the Latin
letter "A", the Cyrillic letter "I", the Chinese character meaning "water", etc. [ Pobierz całość w formacie PDF ]