Due to license restrictions, we ship saxon home edition in wso2 bps. Saxon is used as the xpath runtime for bps. However due to restrictions in saxon home edition, some functionality such as custom xpath extensions would not work out of the box for bps. However, this functionality can be obtained very easily by replacing saxon home edition jar with the saxon professional edition jar.
Following are the steps to do it.
Remove saxon.he_9.4.0.wso2v1.jar from wso2bps-3.0.0/repository/components/plugins directory.
Download Saxon-EE package.
Unzip and copy saxon9ee.jar to wso2bps-3.0.0/repository/components/lib directory.
Copy saxon-license.lic license to wso2bps-3.0.0 directory. ( Saxon license should be obtained from saxonica.com )
Start the server.