The source code is divided into a number of modules which live in the mod directory.

They can be divided into three groups.

• common - modules used by both Jing and Trang
• util - utility functions, some XML-related, some not; used by almost all other modules
• resolver - integrates handling of the various kinds of URI/entity resolver found in the Java platform (e.g. EntityResolver, EntityResolver2, URIResolver, LSResourceResolver)
• catalog - integrates support for OASIS XML Catalogs into the framework provided by the resolver module; uses the Apache XML Commons Resolver
• regex - supports regular expressions using the syntax of W3C XML Schema Part 2; includes code to translate W3C XML Schema regular expressions into java.util.regex regular expressions
• regex-gen - code that generates some of the code in the regex module
• datatype - supports the idea of a datatype library
• xsd-datatype - implements the datatypes of W3C XML Schema Part 2 as a datatype library; depends on the regex and datatype modules
• rng-parse - parses both the XML and compact syntax of RELAX NG
• jing - modules used only by Jing
• pattern - matching and simplifying RELAX NG patterns; depends on datatype, rng-parse; this is the guts of Jing
• rng-jarv - implements the JARV validation interface on top of pattern
• jaxp - provides extensions and helpers for the JAXP javax.xml.validation API
• rng-jaxp - implements the JAXP javax.xml.validation API on top of pattern; uses the jaxp module
• validate - provides a schema language independent framework for validation; this predates the standard javax.xml.validation JAXP interface; eventually this will probably be superseded by the extended JAXP interface defined in the jaxp module
• rng-validate - implements RELAX NG validation for the framework provided by the validate module using the pattern module; depends on datatype, validate, rng-parse, pattern
• nvdl - implements NVDL validation for the framework provided by the validate module; depends on rng-validate (because it uses RELAX NG to validate NVDL schemas); also implements MNS and NRL, the non-standard predecessors to NVDL
• schematron - implements Schematron 1.5 for the framework provided by the validate module; depends on rng-validate (because it uses RELAX NG to validate Schematron schemas)
• xerces - uses Xerces2-J to implement support for W3C XML Schema based on the framework provided by the validate module
• picl - some experimental code for a Path-based Integrity Constraint Language that was being developed for Part 7 of DSDL
• trang - modules used only by Trang
• rng-schema - provides an object model for RELAX NG schemas, which is designed to capture everything about a schema that is significant for a schema author; supports input/output between the object model and RELAX NG XML and compact syntax; depends on rng-parse
• convert-to-xsd - converts from the rng-schema object model to W3C XML Schema
• convert-to-dtd - converts from the rng-schema object model to XML 1.0 DTDs
• dtd-parse - parses XML 1.0 DTDs producing an object model that captures use of parameter entities; note that this doesn't use an external XML parser; depends only on the util module
• dtdinst - an application that generates an XML representation of the dtd-parse object model
• convert-from-dtd - uses the dtd-parse module to convert DTDs into the rng-schema object model
• infer - infers an schema based on one or more XML instances; the schema has expressive level of XML DTDs together with XML Schema Datatypes; depends only on util and datatype
• convert-from-xml - uses the infer module to generate an rng-schema object model from one or more XML instances
• trang - contains the Trang application; this uses the various modules to convert the input format first into the rng-schema object model and then from the rng-schema object model to the output format