XPKG is an innovative XML-based format used for describing software packages, designed with simplicity in mind. It consists currently of 4 specifications: XPKG Metadata, XPKG Dependencies, XPKG Instructions and XPKG Packaging.
XPKG Metadata is XML-based format of describing software package metadata. It's written to support describing multiple versions of package, so it can be used e.g.. in software repositories. It uses XPKG Dependencies, so it has very powerful per-release dependencies support. Also, it can link to installation/updating instructions. It's based on Dublin Core.
XPKG Dependencies is very powerful XML-based markup language of describing dependencies of software packages. It's possible to specify required, suggested, recommended, provided, replaced and conflicting packages, and their versions. It's based on Dublin Core.
XPKG Instructions is XML-based format of describing software installation. It was designed to correct all problems of other instruction formats, like MODX. Its unique features include inserting code in line before, before (in the same line), after (in the same line) and line after, recursive finding, deleting found text, making files writable, running installers and more!
XPKG Packaging is a simple specification describing how to package XPKG packages, so that it will be possible to create XPKG installers and other tools processing them.
XPKG Repository is a planned specification of a repository containing XPKG packages. It will be based on XPKG Metadata.
XPKG files can be validated with any RELAX NG validator supporting compact syntax using correct RNC files - http://xtreeme.org/xpkg/metadata.rnc for XPKG Metadata files and http://xtreeme.org/xpkg/instructions.rnc for XPKG Instructions files. You don't have to install anything - there is Validator.nu.
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We have created a xpkg.xsl file for use with phpBB MODs, you may use it with your MODs. We are also currently creating a sample XPKG MOD, you can see some parts of it: info.xml, install.xml