我收到以下错误：Warning: preg_replace() [function.preg-replace]: No ending delimiter \'.\' found in 但我不明白为什么

代码如下：

foreach( $content as $item )
                {
                    $item = preg_replace( array(\'.\',\' \'), array(\'-\',\'-\'), strtolower($item));
                    $replace = \'<h4 id="\'.utf8_decode($item).\'">\';
                    $phrase = preg_replace(\'/\'.$tag.\'/\', $replace, $phrase, 1);
                }