code: function( onContentOnly, image, autoFireChange )
  		{
  			var snapshots = this.snapshots;
  
  			// Get a content image.
  			if ( !image )
  				image = new Image( this.editor );
  
  			// Do nothing if it was not possible to retrieve an image.
  			if ( image.contents === false )
  				return false;
  
  			// Check if this is a duplicate. In such case, do nothing.
  			if ( this.currentImage && image.equals( this.currentImage, onContentOnly ) )
  				return false;
  
  			// Drop future snapshots.
  			snapshots.splice( this.index + 1, snapshots.length - this.index - 1 );
  
  			// If we have reached the limit, remove the oldest one.
  			if ( snapshots.length == this.limit )
  				snapshots.shift();
  
  			// Add the new image, updating the current index.
  			this.index = snapshots.push( image ) - 1;
  
  			this.currentImage = image;
  
  			if ( autoFireChange !== false )
  				this.fireChange();
  			return true;
  		}
docs: Save a snapshot of document image for later retrieve.