Two things must be understood about the validating parser: method on white space that it knows to be irrelevant.From the standpoint of an application that is interested in processing only the XML data, that is a good thing because the application is never bothered with white space that exists purely to make the XML file readable.
For validation to be possible, the XML document needs to be associated to a DTD or an XML schema. Up until this point, this lesson has concentrated on the non-validating parser.
This section examines the validating parser to find out what happens when you use it to parse the sample program.
The Java XML implementation does so whenever the DTD makes it possible.
The program is configured to take additional arguments when it is started, which tell it to implement no validation, DTD validation, XML Schema Definition (XSD) validation, or XSD validation against a specific schema source file.
On the other hand, if you are writing an application that filters an XML data file and if you want to output an equally readable version of the file, then that white space would no longer be irrelevant: it would be essential.