Thank you for replying. The problem is that our client wants exactly this kind of behavior ( we presented a solution with something similar to the RowEditTemplate and it wasn't satisfactory). I've debuged your javascript code and I think I found a solution. Still have a problem with the add row functionality but i'm investigationg this also and try to come with a solution.

Here is how I've done it, just in case someone else looks for it:

In the server side control use ClientScript to register your js file and to run a startup script that will initialize the client side behavior object.

Something in the lines of : var x = new SearchControl(id);

The client side object ( is not fully implemented just a proof of concept to see that it works):

function SearchControl(id)
{
 this.ID = this.Id = id;
 this.Element = document.getElementById(this.Id);
 this.ClientUniqueId = this.Id;
 
 this.getVisible=function(){return (this.Element.style.display!="none"&&this.Element.style.visibility!="hidden");}
 this.setVisible=function(show,left,top,width,height)
 {
  this.Element.style.display = show ? 'block' : 'none';
  if (show)
  {
    this.Element.style.position = 'absolute';
    this.Element.style.width = width;
    this.Element.style.height = height;
    this.Element.style.top = top;
    this.Element.style.left = left;
  }
 }
 
 this.setValue=function(date,fireEvent)
 {
  alert('setValue');
 }
 
 this.getValue=function(){
  return 'somevalue';
 }
 
 this.handlers = new Array();  
 
 this.addEventListener=function(name,fref,obj)
 {
   var a=this.handlers[name=name.toLowerCase()];
  if(a==null)this.handlers[name]=a=new Array();
  var eh=a[a.length]=new Object();eh.handler=fref;eh.obj=obj;     
 }
 
 this.removeEventListener=function(name,fref,obj)
 {
   name=name.toLowerCase();
  if(this.handlers==null)return;
  if(this.handlers[name]==null||!(this.handlers[name].length))return;
  for(i=0;i<this.handlers[name].length;i++)
  {
    var listener=this.handlers[name][i];
   if(listener!=null)if(listener.handler==fref)this.handlers[name][i]=null;
  }  
 }
 
 this.Element.Object = this; 
 
} 

The UniqueID implementation of the IProvidesEmbeddableEditor must actually return the ClientID of the control.