// function switchDiv()
//  this function takes the id of a div
//  and calls the other functions required
//  to show that div
//
function switchDiv(div_id) {
  var style_sheet = getStyleObject(div_id);
  if (style_sheet)  {
    hideAll();
    changeObjectVisibility(div_id,"visible");
  }  else   { alert("sorry, this only works in browsers that do Dynamic HTML");  }
}

function switchImage(div_id) {
  var style_sheet = getStyleObject(div_id);
  if (style_sheet)  {
    hideImages();
    changeObjectVisibility(div_id,"visible");
  }  else   { alert("sorry, this only works in browsers that do Dynamic HTML");  }
}

// function hideAll()
//  hides a bunch of divs
//
function hideAll() {
   changeObjectVisibility("page1","hidden");
   changeObjectVisibility("page2","hidden");
   changeObjectVisibility("page3","hidden");
   changeObjectVisibility("page4","hidden");
   changeObjectVisibility("page5","hidden");
   changeObjectVisibility("page6","hidden");
   changeObjectVisibility("page7","hidden");
   changeObjectVisibility("page8","hidden");
   changeObjectVisibility("page9","hidden");
   changeObjectVisibility("page10","hidden");
}

function hideImages() {
   changeObjectVisibility("image1","hidden");   
   changeObjectVisibility("image2","hidden");
   changeObjectVisibility("image3","hidden");
   changeObjectVisibility("image4","hidden");
   changeObjectVisibility("image5","hidden");
   changeObjectVisibility("image6","hidden");
   changeObjectVisibility("image7","hidden");
   changeObjectVisibility("image8","hidden");
   changeObjectVisibility("image9","hidden");
   changeObjectVisibility("image10","hidden");
   changeObjectVisibility("image11","hidden");
   changeObjectVisibility("image12","hidden");
   changeObjectVisibility("image13","hidden");
   changeObjectVisibility("image14","hidden");
   changeObjectVisibility("image15","hidden");
}

// function getStyleObject(string) -> returns style object
//  given a string containing the id of an object
//  the function returns the stylesheet of that object
//  or false if it can't find a stylesheet.  Handles
//  cross-browser compatibility issues.
//
function getStyleObject(objectId) {
  // checkW3C DOM, then MSIE 4, then NN 4.
  //
  if(document.getElementById && document.getElementById(objectId)) {
	return document.getElementById(objectId).style;
   }
   else if (document.all && document.all(objectId)) {  
	return document.all(objectId).style;
   } 
   else if (document.layers && document.layers[objectId]) { 
	return document.layers[objectId];
   } else {
	return false;
   }
}

function changeObjectVisibility(objectId, newVisibility) {
    // first get a reference to the cross-browser style object 
    // and make sure the object exists
    var styleObject = getStyleObject(objectId);
    if(styleObject) {
	styleObject.visibility = newVisibility;
	return true;
    } else {
	// we couldn't find the object, so we can't change its visibility
	return false;
    }
}