Web Design in a Nutshell

XML Syntax Basics

Browsers will often recover from sloppily written or illegal HTML. This won’t be the case with XML documents. A client reading an XML document may be reading tags unique to that document and therefore can’t make assumptions about whether or not a tag should be closed. Every XML element must be closed.

Like HTML, XML tags cannot overlap. Overlapping tags look like this:

<Element1><Element2>This is content contained</Element1> in overlapping tags</Element2>

In the above example, it is unclear whether the text, “This is content contained” is an Element 1 or Element 2. To avoid such confusion, an XML document cannot contain overlapping tags. The above example should be written like this:

<Element1><Element2>This is content contained</Element2>
</Element1><Element2> in overlapping tags</Element2>

With this code, there is no question as to which tags or objects are contained within others.

Turning Existing HTML Documents into XML

Because HTML and XML are closely related, it isn’t difficult to make an HTML document XML-compliant. You basically have to make sure your HTML is “well-formed.”

• Replace the DOCTYPE declaration and any internal subset with the XML declaration. Replace:

  <!DOCTYPE HTML ...>

  with:

  <?xml version="1.0" standalone="yes"?>

• Change any empty elements such as <isindex>, <base>, <meta>, <img>, <br>, <hr>, or <spacer> so they end with />, for example:

  <IMG SRC="this_photo.jpg" alt="Photo"/>

  These elements may require some experimentation. For instance, some browsers ...