XHTML - DTD
An XHTML DTD describes the allowed syntax and grammar of XHTML markup. Every XHTML document must start with a DTD declaration and a line of code that declares that you are starting to write XHTML code.
- 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
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"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
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"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
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
Use the frameset DOCTYPE when you want to use HTML frames.
An XHTML document consists of three main parts:
- the DOCTYPE declaration
- the <head> section
- the <body> section
The basic document structure is:
<!DOCTYPE ...>
<html>
<head>
<title>... </title>
</head>
<body> ... </body>
</html>
Note: The DOCTYPE declaration is always the first line in an XHTML document!
This is a simple (minimal) XHTML document:
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>simple document</title>
</head>
<body>
<p>a simple paragraph</p>
</body>
</html>
The DOCTYPE declaration above defines the document type. The rest of the document looks like HTML.
