If we pass 'true' the parser will validate xml documents otherwise not.
The catalog lookup is inserted between the moment the reference is recognized by the software (XML parser, stylesheet processing, or even images referenced for inclusion in a rendering) and the time where loading that resource is actually started.
It is basically used for 3 things: In a normal environment libxml2 will by default check the presence of a catalog in /etc/xml/catalog, and assuming it has been correctly populated, the processing is completely transparent to the document user.
To take a concrete example, suppose you are authoring a Doc Book document, this one starts with the following DOCTYPE definition: When validating the document with libxml, the catalog will be automatically consulted to lookup the public identifier "-//Norman Walsh//DTD Doc Bk XML V3.1.4//EN" and the system identifier " and if these entities have been installed on your system and the catalogs actually point to them, libxml will fetch them from the local disk.
In this section, you will learn to validate a xml file against a DTD (Document Type Definition) using the DOM APIs.
A DTD defines the document structure with a list of legal elements and attributes.
Description of program: Validating a XML file against a DTD needs a xml file and its DTD document.
First of all construct a well-formed xml file along with a DTD file .
This DTD file defines all elements to keep in the xml file.
After creating these, we parse the xml file using the parse() method and generates a Document object tree.