XHTML vs. HTML
Continuing with differentiating XHTML from HTML, in this lesson am going to mention some more rules for XHTML that differs it from HTML.
· Attribute values must be enclosed within double quotations.
· Attribute minimization is not allowed.
· Each XHTML page must have a DTD (Document Type Definition) that describes elements used in the page.
Below examples that illustrate the difference between XHTML and HTML for the above points:
In HTML, you might write something like this:
In XHTML it is not valid, each attribute value must be enclosed within double quotations.
For the second point, attribute minimization is not allowed in XHTML,
For example it is accepted in HTML to write
Or <frame noresize>
Or <input disabled>
All the above are not allowed in XHTML, you cannot abbreviate or minimize attributes,
To be written correctly in XHTML, it must be written like that:
<option checked=”checked” />
<frame noresize=”noresize” />
<input disabled=”disabled” />
Remember that empty tags like above ones that does not have a closing tag are closed by a space followed by a forward slash. />
Document Type Definition DTD:
All XHTML documents must have a DOCTYPE definition that describes the XHTML document, later on this tutorial we’ll talk in deep details about DOCTYPE, but for now am going to point to the structure of an XHTML document that must be used in each XHTML document, this structure must appear in all XHTML documents, and on the order. This structure consists of DOCTYPE declaration, followed by the html, head, title, and body elements. This structure mandatory, and differs from HTML that it must look like that and not optional, like what we saw in the beginning of this tutorial.
According to this rule, the minimum XHTML document looks like this:
<!DOCTYPE doctype definition goes here>
Note that the DOCTYPE is not an XHTML element, so it does not follow XHTML rules for elements. The xmlns attribute of html specifies the xml namespace that is used in the document, it determines the rules of xml that must be followed in this document, this namespace is the default namespace of xml, so it is optional to write it or not, since it will be added automatically to the html tag.
To be continued,
To download this lesson as PDF click here: XHTML Tutorial–Lesson 1 Part II