Returns the item assigned to the given tag.
        
        :param      tag | <str>
        
        :return     <XMultiTagItem> || None

def itemFromTag( self, tag ):
        """
        Returns the item assigned to the given tag.
        
        :param      tag | <str>
        
        :return     <XMultiTagItem> || None
        """
        for row in range(self.count() - 1):
            item = self.item(row)
            if ( item and item.text() == tag ):
                return item
        return None