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HTML Tutorial – 18 – Standards

Every HTML document should begin with a reference to a Document Type Definition (DTD), or doctype, to be standard compliant. This definition declares which version of the HTML standard that the document follows and must be placed before the <html> element. The three versions defined are: strict, transitional and frameset.

Strict definition

The strict definition includes only the structural markup without any of the deprecated elements or attributes. Instead, it leaves formatting up to CSS.


Transitional definition

The transitional definition includes everything that is deprecated and is intended to smooth the transition over to the strict definition.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "">

Frameset definition

The frameset definition is used by frame documents. It contains the same elements as the transitional definition, except that it includes the frameset elements.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "">

XHTML definitions

There are corresponding versions for XHTML documents.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "">
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "">

Meta tag

Another standard that should be followed is to include metadata in the document, using the <meta> header tag. The tag requires either the name or http-equivalent attribute, paired with the content attribute. The http-equivalent attribute will cause the metadata to be sent as HTTP header information. The most important metadata is the document’s file format and its character encoding.

<meta http-equiv="Content-Type" 
content="text/HTML; charset=iso-8859-1">

For XHTML documents another MIME type and subtype are used.

<meta http-equiv="Content-Type" 
content="application/xhtml+xml; charset=iso-8859-1" />

Metadata can also be used to help search engines by providing a description of the document and a list of keywords relating to its content.

<meta name="description" content="document description">
<meta name="keywords" content="list, of, keywords">

Another common use of the <meta> tag is to automatically redirect a visitor to a new page after a specific number of seconds.

<meta http-equiv="refresh" content="0; url=newpage.html">