[ Mike Brown]
Passin, Tom wrote:
From the DTD in the HTML 4.01 Rec -
<!ELEMENT HEAD O O (%head.content;) +(%head.misc;) -- document head
--> <!ELEMENT TITLE - - (#PCDATA) -(%head.misc;) --
document title -->
<!ELEMENT HTML O O (%html.content;) -- document root element -->
<!ELEMENT BODY O O (%block;|SCRIPT)+ +(INS|DEL) -- document body -->
Very clear, right? Those tags are optional. Aren't you glad you
don't have to design the parser?
Heh. OK, I was wrong.
However, the prose in section 7.1 says
An HTML 4 document is composed of three parts:
1. a line containing HTML version information,
2. a declarative header section (delimited by the HEAD element),
3. a body, which contains the document's actual content.
The body may be
implemented by the BODY element or the FRAMESET element.
White space (spaces, newlines, tabs, and comments) may
appear before or
after each section. Sections 2 and 3 should be delimited by
the HTML
element.
I see we're back in the should/may/must discussion, but at
the very least it sounds like HEAD is not optional, based on
that prose, and it sounds like
one of either BODY or FRAMESET are required.
There is a distinction - these **elements** do have to be present but
they do **not** have to be delimited by opening and closing tags. For
example, given an html document the parser knows that it has to start
out with the head element. The first time it sees an element that
belongs only in the body, like an <h1>, it knows that the head element
has terminated. The SGML DTD syntax tells you which **tags** have to be
present when you put in an element. The "O" indicates an optional tag,
the "-" indicates a mandatory tag.
XML parsing is much simpler because there are no optional tags. SGML
can be much more complicated.
Cheers,
Tom P
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