This section defines the term document, and provides additional details related to the definition of that term. It is divided into the following parts:
The term document is used in this reference to mean an instance of the HTML language.
The HTML language is the language described in this reference; it is an abstract language that applications can potentially represent in memory in any number of possible ways, and that can be transmitted using any number of possible concrete syntaxes.
This reference describes two particular concrete syntaxes for the HTML language: One syntax, which is referred to throughout this reference as the HTML syntax, and another syntax, which is referred to throughout this reference as the XML syntax. Web browsers typically implement two separate parsers for processing documents: an HTML parser which is invoked when processing documents in the HTML syntax, and an XML parser which is invoked when processing documents in the XML syntax.
The HTML syntax is the syntax described in the HTML syntax section of this reference.
The XML syntax is defined by rules in the [XML] specification and in the [Namespaces In XML] specification; any syntax-level requirements for documents in the XML syntax described in this reference are intended to be the same as those defined in the XML specification.
The
HTML namespace
is defined as http://www.w3.org/1999/xhtml.
The HTML namespace is the
namespace both for
documents in the HTML syntax
and for
documents in the XML syntax.
Documents that are served with the
text/html MIME type
must
match the descriptions in this
reference for characteristics of
documents in the HTML syntax.
Documents that have an
HTML namespace
declaration and that are served with an XML MIME type
such as
text/xml,
application/xml, or
application/xhtml+xml
must
match the descriptions in this
reference for characteristics of
documents in the XML syntax.
There are two types of conformant documents:
A conformant document in the HTML syntax must consist of the following parts, in the following order:
The start tag and end tag of the html element can be omitted—as well as, possibly, the start tags and end tags of certain descendants of the html element—in which case the start tag and end tag are considered to be implied.
Documents in the HTML syntax must match the syntax described in the HTML syntax section of this reference.
In documents in the HTML syntax, the start tags and end tags of the html element and particular descendants of the html element can be omitted. In cases where tag omission of those particular elements occurs, the document can still be considered, conceptually, to contain the elements—but with their start tags and end tags implied.
The following is an example of a document with implied start tags and end tags for the html, head, and body elements. Note that it is nevertheless a complete, valid document.
<!DOCTYPE html> <title>A relatively minimal HTML document</title> <p>Hello World!</p>
The DOM tree constructed from that example by a conformant UA would look like this:
htmlHTML
HEAD
TITLE
#text: A relatively minimal HTML document#text: ↩ BODY
P
#text: Hello World!Note that the DOM tree includes the html, head, and body elements whose start tags and end tags are implied in the document.
A conformant document in the XML syntax must be a namespace-well-formed XML document, as defined in the [Namespaces in XML] specification, and its root element must be an html element.
Documents in the XML syntax must not make use of any features of the HTML syntax that do not follow XML well-formedness constraints (for example, documents in the XML syntax must not use unquoted attribute value syntax and must not omit tags).
In documents in the HTML syntax:
In documents in the XML syntax: