code: def getFieldDescription(self, fieldName):
      
  
      # Find which field it's in
      description = self.getDescription() + [("end", self.getWidth())]
      for i in xrange(len(description)):
        (name, offset) = description[i]
        if (name == fieldName):
          break
  
      if i >= len(description)-1:
        raise RuntimeError("Field name %s not found in this encoder" % fieldName)
  
      # Return the offset and width
      return (offset, description[i+1][1] - offset)
docs: Return the offset and length of a given field within the encoded output.
  
      :param fieldName: Name of the field
      :return: tuple(``offset``, ``width``) of the field within the encoded output