There's more...

There are many things to say about the XML ecospace. There are XML engines that provide facilities to search data in an XML tree (XPath), to validate XML using other XML (XML Schema or DTD), to transform an XML into another kind of format using another XML (XSLT), and many others (http://en.wikipedia.org/wiki/List_of_XML_markup_languages). The good thing is that just like XML, the DOM object is also standardized. So, every library that is compliant with the standard has the same methods, from Delphi to JavaScript and from Python to C#.

TXMLDocument allows you to select the DOMVendor implementation. By default, there are three implementations available:

• MSXML:
  • From Microsoft; implemented as COM objects
  • Supports XML transformations
  • Available only on Windows (so no Android, iOS, or Mac OS X)
• Omni XML:
  • Much faster than ADOM and based on the Open Source Project.
  • It is cross-platform, so is available on all the supported Delphi platforms. If you plan to write XML handling code on mobile or Mac, this is the way to go.
• ADOM XML:
  • A quite old open source Delphi implementation
  • Does not support transformations
  • Available on all supported Delphi platforms
  • For backward compatibility, consider Omni XML instead in Delphi

TXMLDocument uses a Windows-only vendor by default. If you are designing a FireMonkey application that is intended to run on other platforms than Windows, select a cross-platform DOM vendor.

XSLT allows you to transform XML to something else, using other XML as a stylesheet. As we saw in this recipe, you can use an XML file and an XSLT file to generate an HTML page that shows the data contained in the XML, using XSLT to format the data.

The following function loads one XML and one XSLT document from two string variables. Then, we use the XSLT document to transform the XML document. The code that follows shows this in detail:

function Transform(XMLData: string; XSLT: string): String; 
var 
  LXML, LXSL: IXMLDocument; 
  LOutput: WideString; 
begin 
  LXML := LoadXMLData(XMLData); 
  LXSL := LoadXMLData(XSLT); 
  LXML.DocumentElement.TransformNode( 
    LXSL.DocumentElement, LOutput); 
  Result := String(LOutput); 
end; 

This function doesn't know about the output format because it is defined by the XSLT document. The result could be XML, HTML, CSV, plain text, or whatever the XSLT defines, but the code does not change.

XSLT can be really useful. I recommend that you go and visit http://www.w3schools.com/xml/xsl_languages.asp for further details on the language.