The most common DTD is XHTML Transitional.
Is Mandatory
An XHTML document consists of three main parts:
the DOCTYPE declaration
the
the section
The basic document structure is:
Note: The DOCTYPE declaration is always the first line in an XHTML document!
An XHTML Example
This is a simple (minimal) XHTML document:
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
a simple paragraph
The DOCTYPE declaration above defines the document type. The rest of the document looks like HTML.
Document Type Definitions (DTD)
A DTD specifies the syntax of a web page in SGML
DTDs are used by SGML applications, such as HTML, to specify rules for documents of a particular type, including a set of elements and entity declarations
An XHTML DTD describes in precise, computer-readable language, the allowed syntax of XHTML markup
There are three XHTML DTDs:
STRICT
TRANSITIONAL
FRAMESET
XHTML 1.0 Strict
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
Use the strict DOCTYPE when you want really clean markup, free of presentational clutter. Use it together with CSS.
XHTML 1.0 Transitional
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
Use the transitional DOCTYPE when you want to still use HTML’s presentational features.
XHTML 1.0 Frameset
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
Use the frameset DOCTYPE when you want to use HTML frames.
