This is THE top level container element for an HTML document.
It specifies that the content of the document is text with HTML markup
tags. The content of an HTML document is a HEAD element which contains
the title of the document plus other information ABOUT the
document. Following the HEAD element comes the visible content of the
document in the BODY element. Alternately, an author may specify a
FRAMESET series in place of the BODY element that enumerates the
layout of sub-documents to be contained in the master document.
This is an SGML Document Access
(SDA) attribute. SDA attributes are designed to transform HTML (and
other SGML-based documents) to the ICADD
DTD - which is used in creating accessible documents for users with
visual disabilities (rendering in Braille, large print, speech
synthesis, etc.) The attribute value specifies the name of the element
to convert this element to in the SDA element group (in this case the
'Book' element - "highest level element for document".) SDA also allows
attributes and values from the original element to be used in the new
SDA element where necessary.
Value:Book (Denotes 'highest level element for document' in SDA.)
This is a quoted string called a Formal Public Identifier (FPI.) Every distinct
DTD variation will have its own unique FPI string. For more on FPIs, see the
!Doctype element. Using this string appears to
take the place of the !Doctype element.
"-//W3C//DTD HTML 4.0//EN"
"-//W3C//DTD HTML 4.0 Transitional//EN"
"-//W3C//DTD HTML 4.0 Frameset//EN"
The HTML element was not a required element in the HTML specifications (but it is required
under XHTML), and most popular browsers will not react oddly to its absence.
Still, this is a basic top level element in the HTML/XHTML document structure
and it is recommended to use it.
Netscape 6, Beta 1 did not support CSS attached via the HTML element.
This was fixed in N6B2 and above.