An approximate GedcomX Date.
Inherits from Simple.
function Approximate() {

  if(arguments.length > 0) {

    if(arguments[0].length < 1 || arguments[0].charAt(0) != 'A') {
      throw new Error('Invalid Approximate Date');
    }
    try {
      Simple.call(this, arguments[0].substr(1));
    } catch(e) {
      throw new Error(e.message+' in Approximate Date');
    }
  } else {
    Simple.call(this);
  }
}