anchor.diff:  Offset=8
   Field1=123456
   Field2=AB
  -dump> <fsdmsgX name="Example1">
  -dump>   <field id="Field1" value="123456"/>
  -dump>   <field id="Field2" value="AB"/>
  -dump> </fsdmsgX>
  -tree> [Example1]
  -tree> Field [Field1] : Fixed [6] : 123456
  -tree> Field [Field2] : Fixed [2] : AB
  +dump<fsdmsgX name="Example1">
  +dump	<field id="Field1" value="123456"/>
  +dump	<field id="Field2" value="AB"/>
  +dump</fsdmsgX>
  +tree>[Example1]
  +tree>Field [Field1] : Fixed [6] : 123456
  +tree>Field [Field2] : Fixed [2] : AB
   0000  31 32 33 34 35 36 41 42                           123456AB
  +
  +
  +
  +
  +
   
   * Create the main container object FSDMsgX.
   * Create the individual field packagers for field1 and field2.
  
positive.code: * See the hexdumps are identical for both the containers,operations show equivalence.
  
  
  ===== BranchFieldPackager
  
  Consider a specification where you need to parse fields differently based on a particular field. Typically you will see a pattern where, if the value of the field is X the fields following it are Y1,Y2..Yn.
  
  
negative.code: * The container has a hexdump method that dumps the hex equivalent of the unpacked stream. Notice EXTRA is not there as there was no rule to unpack it.
  * If the input string was s = "123456" then an ISOException would be thrown telling you precisely what was wrong.
  org.jpos.iso.ISOException: Field [Field2] at offset [6]:Expecting 2 bytes found 0
  	
  
  .FixedFieldPackager Usage [packing object into bytes]
  ====
  
  		
  		FSDMsgX msg = new FSDMsgX("Example1");
  		FixedFieldPackager field1 = new FixedFieldPackager("Field1", 6, AsciiInterpreter.INSTANCE);
  		FixedFieldPackager field2 = new FixedFieldPackager("Field2", 2, AsciiInterpreter.INSTANCE);
  
  		msg.add(field1);
  		msg.add(field2);
  
  		msg.set("Field1", "ABCDEF");
  		msg.set("Field2", "12");
  	
  		byte[] outStream = msg.pack();
  	
  		System.out.println(msg.dump("dump"));
  		System.out.println(msg.getParserTree("tree>"));
  		System.out.println(msg.hexDump(""));
  		System.out.println(ISOUtil.hexdump(outStream));
  
  	
  
  ====
  
  *Output*
  [source,xml]
  dump<fsdmsgX name="Example1">
  dump	<field id="Field1" value="ABCDEF"/>
  dump	<field id="Field2" value="12"/>
  dump</fsdmsgX>
  tree>[Example1]
  tree>Field [Field1] : Fixed [6] : ABCDEF
  