Bjorn Reese is the author of the number support and worked on the
XSLTMark support
William Brack was an early adopted, contributed a number of patches and
spent quite some time debugging non-trivial problems in early versions of
libxslt
If you want to use libxslt in a Mac OS X/Cocoa or Objective-C
framework, Marc Liyanage provides an application
TestXSLT for XSLT and XML editing including wrapper classes for the
XML parser and XSLT processor.