HTML pages uses predefined tags, and the meaning of these tags is well understood:
<p> means a paragraph and <h1> means a header, and the browser knows
how to display these pages.
With XML we can use any tags we want,
and the meaning of these tags are not automatically understood by the browser:
<table> could mean a HTML table or maybe a piece of
furniture. Because of the nature of XML, there is no standard way to display an
XML document.
In order to display XML documents, it is necessary to have a
mechanism to describe how the document should be displayed. One of these
mechanisms is Cascading Style Sheets (CSS), but XSL (eXtensible Stylesheet Language) is the
preferred style sheet language of XML, and XSL
is far more sophisticated than the CSS used by HTML.
XSL - More than a Style Sheet
XSL
consists of two parts:
a method for transforming XML documents
a method for formatting XML documents
If you don't understand the meaning of this, think of XSL as a language that
can transform XML into HTML, a language that can filter and sort XML
data and a language that can format XML data, based on the data value,
like displaying negative numbers in red.
XSL - What can it do?
XSL can be used to define how an XML file should be displayed by transforming
the XML file into a format that is recognizable to a browser. One such format is
HTML. Normally XSL does this by transforming each XML element into an HTML
element.
XSL can also add completely new elements into the output file, or remove
elements. It can rearrange and sort the elements, test and make decisions
about which elements to display, and a lot more.
A note about XSL in IE5
XSL in Internet Explorer 5.0 is not 100% compatible with the latest released
W3C XSL standard. That is because IE 5 was released before the standard was
completely settled. Microsoft has promised to
solve this problem in the 5.5 release.