code: function ProgressSpinner(id, anchor){
  		if(id === undefined){ throw new Error("Missing reqired argument: id"); }
  		if(anchor === undefined){ throw new Error("Missing reqired argument: anchor"); }
  		
  		this._id = id;
  		this._anchor = anchor;
  		
  		// we add a prefix for the id label
  		this._prefix = "progressSpinner:";
  	}
docs: Progress indicator in form of a simple spinner.
  
  @param id [required] unique identifier, e.g. the row number in which the spinner is created
  @param anchor [required] father DOM node for the created spinner
  
  @returns ProgressSpinner object