The SVN repository is public and everyone has read access. The repository uses a standard SVN layout of:
xerces/java/ | | - branches/ | | - tags/ \ - trunk/
In short:
1) to check out the trunk of xerces/java:
svn co https://svn.apache.org/repos/asf/xerces/java/trunk
2) to check out the code tagged with the Xerces-J_2_9_0 tag:
svn co https://svn.apache.org/repos/asf/xerces/java/tags/Xerces-J_2_9_0/
3) to check out the code in the stax-dev/ branch:
svn co https://svn.apache.org/repos/asf/xerces/java/branches/stax-dev/