public function concat($name, $value = null, $mode = ViewBlock::APPEND)
    {
        if ($value === null) {
            $this->start($name, $mode);

            return;
        }

        if (!isset($this->_blocks[$name])) {
            $this->_blocks[$name] = '';
        }
        if ($mode === ViewBlock::PREPEND) {
            $this->_blocks[$name] = $value . $this->_blocks[$name];
        } else {
            $this->_blocks[$name] .= $value;
        }
    }