package.xml 2.0 introduced the new tags<phprelease>, <extsrcrelease>, and<extbinrelease> to differentiate between the different kinds of packages the PEAR installer handles. package.xml 2.1 introduces<zendextsrcrelease> and <zendextbinrelease> in order to differentiate between regular PHP extensions and Zend extensions like xdebug (http://pecl.php.net/xdebug).
You may have noticed that the primary tag in package.xml 1.0 is named<filelist>, whereas the primary tag in package.xml 2.0 is named<contents>. This change came about as a result of a simple feature request. When PEAR 1.3.3 was popular, the need to customize installations grew; more and more attributes and information were crammed into the<file> tag. The platform attribute tells the installer that a file should only be installed on a particular platform, such as UNIX or Windows. This is used in the PEAR package in order to install the pear command using a schell...
