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. 
abstract class javax.xml.xpath.XPathFactoryFinder$SingleIterator implements java.util.Iterator
  minor version: 0
  major version: 59
  flags: flags: (0x0420) ACC_SUPER, ACC_ABSTRACT
  this_class: javax.xml.xpath.XPathFactoryFinder$SingleIterator
  super_class: java.lang.Object
{
  private boolean seen;
    descriptor: Z
    flags: (0x0002) ACC_PRIVATE

  private void <init>();
    descriptor: ()V
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=3, locals=1, args_size=1
        start local 0 // javax.xml.xpath.XPathFactoryFinder$SingleIterator this
         0: .line 58
            new java.lang.Error
            dup
            ldc "Unresolved compilation problems: \n\t'_' is a keyword from source level 9 onwards, cannot be used as identifier\n\t'_' is a keyword from source level 9 onwards, cannot be used as identifier\n"
            invokespecial java.lang.Error.<init>:(Ljava/lang/String;)V
            athrow
        end local 0 // javax.xml.xpath.XPathFactoryFinder$SingleIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Ljavax/xml/xpath/XPathFactoryFinder$SingleIterator;

  public final void remove();
    descriptor: ()V
    flags: (0x0011) ACC_PUBLIC, ACC_FINAL
    Code:
      stack=3, locals=1, args_size=1
        start local 0 // javax.xml.xpath.XPathFactoryFinder$SingleIterator this
         0: .line 306
            new java.lang.Error
            dup
            ldc "Unresolved compilation problem: \n"
            invokespecial java.lang.Error.<init>:(Ljava/lang/String;)V
            athrow
        end local 0 // javax.xml.xpath.XPathFactoryFinder$SingleIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Ljavax/xml/xpath/XPathFactoryFinder$SingleIterator;

  public final boolean hasNext();
    descriptor: ()Z
    flags: (0x0011) ACC_PUBLIC, ACC_FINAL
    Code:
      stack=3, locals=1, args_size=1
        start local 0 // javax.xml.xpath.XPathFactoryFinder$SingleIterator this
         0: .line 307
            new java.lang.Error
            dup
            ldc "Unresolved compilation problem: \n"
            invokespecial java.lang.Error.<init>:(Ljava/lang/String;)V
            athrow
        end local 0 // javax.xml.xpath.XPathFactoryFinder$SingleIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Ljavax/xml/xpath/XPathFactoryFinder$SingleIterator;

  public final java.lang.Object next();
    descriptor: ()Ljava/lang/Object;
    flags: (0x0011) ACC_PUBLIC, ACC_FINAL
    Code:
      stack=3, locals=1, args_size=1
        start local 0 // javax.xml.xpath.XPathFactoryFinder$SingleIterator this
         0: .line 308
            new java.lang.Error
            dup
            ldc "Unresolved compilation problem: \n"
            invokespecial java.lang.Error.<init>:(Ljava/lang/String;)V
            athrow
        end local 0 // javax.xml.xpath.XPathFactoryFinder$SingleIterator this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Ljavax/xml/xpath/XPathFactoryFinder$SingleIterator;

  protected abstract java.lang.Object value();
    descriptor: ()Ljava/lang/Object;
    flags: (0x0404) ACC_PROTECTED, ACC_ABSTRACT
}
SourceFile: "XPathFactoryFinder.java"
NestHost: javax.xml.xpath.XPathFactoryFinder
InnerClasses:
  private abstract SingleIterator = javax.xml.xpath.XPathFactoryFinder$SingleIterator of javax.xml.xpath.XPathFactoryFinder