function Part(textarea) {
  Part.parts.push(this);
  this.textarea = textarea;
  this.textarea.style.overflow = 'hidden';

  this.element = document.createElement('div');

  var s = this.element.style;
  var getStyle = YAHOO.util.Dom.getStyle;
  s.visibility = 'hidden';
  s.position = 'absolute';
  s.zIndex = '1';
  s.fontFamily = getStyle(this.textarea, 'fontFamily');
  s.fontSize = getStyle(this.textarea, 'fontSize');
  s.fontStyle = getStyle(this.textarea, 'fontStyle');
  s.fontVariant = getStyle(this.textarea, 'fontVariant');
  s.lineHeight = getStyle(this.textarea, 'lineHeight');
  this.textarea.parentNode.insertBefore(this.element, this.textarea);
  this.copyToElement();
  this.resizeTextarea();
}

Part.parts = [];

Part.prototype.copyToElement = function() {
  this.element.innerHTML = this.textarea.value.replace(/\n/g,'<br />') + '&nbsp;';
};

Part.prototype.resizeTextarea = function() {
  this.copyToElement();
  this.syncRegions();
  this.setTimeout();
};

Part.prototype.setTimeout = function() {
  var thisC = this;
  this.timeout = setTimeout(function() {thisC.resizeTextarea();}, 500);      
};

Part.prototype.syncRegions = function() {
  var a = parseInt(YAHOO.util.Dom.getStyle(this.textarea, 'fontSize').split('px',1)[0], 10);
  var rt =  YAHOO.util.Dom.getRegion(this.textarea);
  this.element.style.width = (rt.right-rt.left)+'px';
  var re =  YAHOO.util.Dom.getRegion(this.element);
  this.textarea.style.height = (re.bottom-re.top+a*1.6)+'px';
};


function find_parts() {
  var the_form = document.getElementById('comments_form');
  var es = the_form.elements;
  for (var i=0; i<es.length; i++) {
    if (es[i].tagName.toLowerCase() !== 'textarea') {continue;}
    new Part(es[i]);
  }
}
YAHOO.util.Event.addListener(window, "load", find_parts);