code: function startNestedEditableIterator( parentIterator, blockTag, editablesContainer, remainingEditables ) {
  		var editable = getNestedEditableIn( editablesContainer, remainingEditables );
  
  		if ( !editable )
  			return 0;
  
  		var filter = CKEDITOR.filter.instances[ editable.element.data( 'cke-filter' ) ];
  
  		// If current editable has a filter and this filter does not allow for block tag,
  		// search for next nested editable in remaining ones.
  		if ( filter && !filter.check( blockTag ) )
  			return startNestedEditableIterator( parentIterator, blockTag, editablesContainer, editable.remaining );
  
  		var range = new CKEDITOR.dom.range( editable.element );
  		range.selectNodeContents( editable.element );
  
  		var iterator = range.createIterator();
  		// This setting actually does not change anything in this case,
  		// because entire range contents is selected, so there're no <br>s to be included.
  		// But it seems right to copy it too.
  		iterator.enlargeBr = parentIterator.enlargeBr;
  		// Inherit configuration from parent iterator.
  		iterator.enforceRealBlocks = parentIterator.enforceRealBlocks;
  		// Set the activeFilter (which can be overriden when this iteator will start nested iterator)
  		// and the default filter, which will make it possible to reset to
  		// current iterator's activeFilter after leaving nested editable.
  		iterator.activeFilter = iterator.filter = filter;
  
  		parentIterator._.nestedEditable = {
  			element: editable.element,
  			container: editablesContainer,
  			remaining: editable.remaining,
  			iterator: iterator
  		};
  
  		return 1;
  	}
docs: Looks for a first nested editable after previousEditable (if passed) and creates nested iterator for it.