http://xml.apache.org/commons/components/external/: xml-commons provides an Apache-hosted set of DOM, SAX, and JAXP interfaces for use in other xml-based projects. Our hope is that we can standardize on both a common version and packaging scheme for these critical XML standards interfaces to make the lives of both our developers and users easier. The External Components portion of xml-commons contains interfaces that are defined by external standards organizations. For DOM, that's the W3C; for SAX it's David Megginson and sax.sourceforge.net; for JAXP it's Sun. 
public interface javax.xml.xpath.XPathFunctionResolver
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: javax.xml.xpath.XPathFunctionResolver
  super_class: java.lang.Object
{
  public abstract javax.xml.xpath.XPathFunction resolveFunction(javax.xml.namespace.QName, int);
    descriptor: (Ljavax/xml/namespace/QName;I)Ljavax/xml/xpath/XPathFunction;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
    MethodParameters:
              Name  Flags
      functionName  
      arity         
}
SourceFile: "XPathFunctionResolver.java"