HTML and SGML
This section describes the relationship
between HTML and SGML, and guides
the newcomer through interpretation
of the DTD . (This is not a full
tutorial on SGML, and in the event
of any apparent conflict, the SGML
standard is definitive.)
The HyperText Markup Language is
an application conforming to International
Standard ISO 8879 -- Standard Generalized
Markup Language [ SGML ]. SGML is
a system for defining structured
document types, and markup languages
to represent instances of those document
types.
Every SGML document has three parts:
- An SGML declaration, which binds
SGML processing quantities and syntax
token names to specific values. For
example, the SGML declaration in
the HTML DTD specifies that the string
that opens a tag is </ and the maximum
length of a name is 34 characters.
- A prologue including one or more
document type declarations, which
specifiy the element types, element
relationships and attributes, and
references that can be represented
by markup. The HTML DTD specifies,
for example, that the HEAD element
contains at most one TITLE element.
- An instance, which contains the data
and markup of the document.
We use the term HTML to mean both
the document type and the markup
language for representing instances
of that document type.
The SGML declaration for HTML is
given in the appendix ``SGML Delcaration
for HTML.'' It is implicit among
WWW implementations.
The prologue for an HTML document
should look like:
<!DOCTYPE HTML PUBLIC "-//W3 Organization//DTD W3 HTML 2.0//EN">
- NOTE 2:
- Many extant HTML documents
do not contain a prologue. Implementations
are encouraged to infer the above
prologue if the document does not
begin with <! .
.