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 class javax.xml.xpath.XPathConstants
  minor version: 0
  major version: 59
  flags: flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: javax.xml.xpath.XPathConstants
  super_class: java.lang.Object
{
  public static final javax.xml.namespace.QName NUMBER;
    descriptor: Ljavax/xml/namespace/QName;
    flags: (0x0019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL

  public static final javax.xml.namespace.QName STRING;
    descriptor: Ljavax/xml/namespace/QName;
    flags: (0x0019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL

  public static final javax.xml.namespace.QName BOOLEAN;
    descriptor: Ljavax/xml/namespace/QName;
    flags: (0x0019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL

  public static final javax.xml.namespace.QName NODESET;
    descriptor: Ljavax/xml/namespace/QName;
    flags: (0x0019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL

  public static final javax.xml.namespace.QName NODE;
    descriptor: Ljavax/xml/namespace/QName;
    flags: (0x0019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL

  public static final java.lang.String DOM_OBJECT_MODEL;
    descriptor: Ljava/lang/String;
    flags: (0x0019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL
    ConstantValue: "http://java.sun.com/jaxp/xpath/dom"

  static void <clinit>();
    descriptor: ()V
    flags: (0x0008) ACC_STATIC
    Code:
      stack=4, locals=0, args_size=0
         0: .line 44
            new javax.xml.namespace.QName
            dup
            ldc "http://www.w3.org/1999/XSL/Transform"
            ldc "NUMBER"
            invokespecial javax.xml.namespace.QName.<init>:(Ljava/lang/String;Ljava/lang/String;)V
            putstatic javax.xml.xpath.XPathConstants.NUMBER:Ljavax/xml/namespace/QName;
         1: .line 51
            new javax.xml.namespace.QName
            dup
            ldc "http://www.w3.org/1999/XSL/Transform"
            ldc "STRING"
            invokespecial javax.xml.namespace.QName.<init>:(Ljava/lang/String;Ljava/lang/String;)V
            putstatic javax.xml.xpath.XPathConstants.STRING:Ljavax/xml/namespace/QName;
         2: .line 58
            new javax.xml.namespace.QName
            dup
            ldc "http://www.w3.org/1999/XSL/Transform"
            ldc "BOOLEAN"
            invokespecial javax.xml.namespace.QName.<init>:(Ljava/lang/String;Ljava/lang/String;)V
            putstatic javax.xml.xpath.XPathConstants.BOOLEAN:Ljavax/xml/namespace/QName;
         3: .line 65
            new javax.xml.namespace.QName
            dup
            ldc "http://www.w3.org/1999/XSL/Transform"
            ldc "NODESET"
            invokespecial javax.xml.namespace.QName.<init>:(Ljava/lang/String;Ljava/lang/String;)V
            putstatic javax.xml.xpath.XPathConstants.NODESET:Ljavax/xml/namespace/QName;
         4: .line 72
            new javax.xml.namespace.QName
            dup
            ldc "http://www.w3.org/1999/XSL/Transform"
            ldc "NODE"
            invokespecial javax.xml.namespace.QName.<init>:(Ljava/lang/String;Ljava/lang/String;)V
            putstatic javax.xml.xpath.XPathConstants.NODE:Ljavax/xml/namespace/QName;
         5: .line 77
            return
      LocalVariableTable:
        Start  End  Slot  Name  Signature

  private void <init>();
    descriptor: ()V
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // javax.xml.xpath.XPathConstants this
         0: .line 37
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
            return
        end local 0 // javax.xml.xpath.XPathConstants this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Ljavax/xml/xpath/XPathConstants;
}
SourceFile: "XPathConstants.java"