Listens for tab/backtab to modify list information.
        
        :param      event | <QKeyPressEvent>

def eventFilter(self, object, event):
        """
        Listens for tab/backtab to modify list information.
        
        :param      event | <QKeyPressEvent>
        """
        if event.type() != event.KeyPress:
            return super(XRichTextEdit, self).eventFilter(object, event)
        
        cursor    = object.textCursor()
        curr_list = cursor.currentList()
        
        # make sure we're in a current list
        if not curr_list:
            return super(XRichTextEdit, self).eventFilter(object, event)
        
        # unindent for Backtab (Shift+Tab)
        if event.key() == Qt.Key_Backtab:
            delta = -1
        
        # indent for Tab
        elif event.key() == Qt.Key_Tab:
            delta = 1
        
        # otherwise, don't bother calculating
        else:
            return super(XRichTextEdit, self).eventFilter(object, event)
        
        # look for the proper list to move to
        curr_block      = cursor.block()
        curr_indent     = curr_list.format().indent()
        curr_style      = curr_list.format().style()
        prev_block      = curr_block
        next_block      = curr_block
        add_to_list     = None
        add_to_indent   = curr_indent + delta
        
        while prev_block or next_block:
            if prev_block:
                prev_block = prev_block.previous()
                prev_list  = prev_block.textList()
                
                if not prev_list:
                    prev_block = None
                
                else:
                    prev_indent = prev_list.format().indent()
                    
                    if prev_indent == add_to_indent:
                        add_to_list = prev_list
                        break
                    
            if next_block:
                next_block = next_block.next()
                next_list  = next_block.textList()
                
                if not next_list:
                    next_block = None
                
                else:
                    next_indent = next_list.format().indent()
                    
                    if next_indent == add_to_indent:
                        add_to_list = next_list
                        break
        
        if add_to_list is None and 0 < delta:
            if curr_style in (QTextListFormat.ListCircle,
                              QTextListFormat.ListDisc,
                              QTextListFormat.ListSquare):
                self.insertUnorderedList()
            else:
                self.insertOrderedList()
        
        elif add_to_list:
            add_to_list.add(curr_block)
        
        return True