# Usage of Castor and XML parsers

Being an XML data binding framework by definition, Castor XML relies on the availability of an XML parser at run-time. In Java, an XML parser is by default accessed though either the DOM or the SAX APIs: that implies that the XML Parser used needs to comply with either (or both) of these APIs.

With the creation of the JAXP API (and its addition to the Java language definition as of Java 5.0), Castor internally has been enabled to allow usage of the JAXP interfaces to interface to XML parsers. As such, Castor XML allows the use of a JAXP-compliant XML parser as well.

By default, Castor ships with Apache Xerces 2.6.2. You may, of course, upgrade to a newer version of Apache Xerces at your convenience, or switch to any other XML parser as long as it is JAXP compliant or implements a particular SAX interface. Please note that users of Java 5.0 and above do not need to have Xerces available at run-time, as JAXP and Xerces have both been integrated into the run-time library of Java.

For marshalling, Castor XML can equally use any JAXP complaint XML parser (or interact with an XML parser that implements the SAX API), with the exception of the following special case: when using 'pretty printing' during marshalling (by setting the corresponding property in `castor.properties` to `true`) with Java 1.4 or below, Apache Xerces has to be on the classpath, as Castor XML internally uses Xerces' `XMLSerializer` to implement this feature.

The following table enlists the requirements relative to the Java version used in your environment.

## XML APIs on various Java versions

Java 1.4 and below | Java 5.0 and above
Xerces 2.6.2 | -
XML APIs | -