public Attr(String name,String value){
  _name=name.toLowerCase();
  _stringValues=new ArrayList<>(1);
  _stringValues.add(value);
}

public Attr ( String name , String value ) { _name = name . toLowerCase ( ) ; _stringValues = new ArrayList < > ( 1 ) ; _stringValues . add ( value ) ; }
construct an attribute value pair with a single string value .
