Help with 2 errors using DOMDocument for html parsing

When I run the decorate_keyword() function below, I'm getting two errors that I'm trying to resolve. The first seems the easiest to resolve. I'm getting...

Warning: DOMXPath::query() [domxpath.query]: Invalid expression in C:\xampplite\htdocs\testsite\wp-content\plugins\myplugin\index.php on line 48

Which points to the $nodes line in the function and is apparently stemming from the $keyword variable when it contains an empty space. $keyword = "test" does not throw the error. What do I need to change to overcome this error?

function rseo_decorate_keyword($postarray) {
    $keyword = "test";
    $content = $postarray['post_content'];
    /* 
     even though I can echo $content and get a string, 
     I'm getting error: Empty string supplied in loadHTML() when I use this. 
     so, I have to explicity set it to a string as below to test.
   */
    $content = "this is a test phrase";
    $d = new DOMDocument();
    $d->loadHTML($content);
    $x = new DOMXpath($d);
    $nodes = $x->query("//text()[contains(.,$keyword) and not(ancestor::h1) and not(ancestor::h2) and not(ancestor::h3) and not(ancestor::h4) and not(ancestor::h5) and not(ancestor::h6)]");
    if ($nodes && $nodes->length) {
        $node = $nodes->item(0);
        // Split just before the keyword
        $keynode = $node->splitText(strpos($node->textContent, $keyword));
        // Split after the keyword
        $node->nextSibling开发者_如何学Python->splitText(strlen($keyword));
        // Replace keyword with <b>keyword</b>
        $replacement = $d->createElement('b', $keynode->textContent);
        $keynode->parentNode->replaceChild($replacement, $keynode);
    }
     $postarray['post_content'] = $d;
return $postarray;
}

The contains XPath function should have the second argument in quotes if it contains various characters, such as ;&,. The space is one of them.

$nodes = $x->query("//text()[contains(.,'$keyword') and not(ancestor::h1) and not(ancestor::h2) and not(ancestor::h3) and not(ancestor::h4) and not(ancestor::h5) and not(ancestor::h6)]");

For your mysql_real_escape_string error, for some reason an object is being passed rather than a string. I'm not familiar with Wordpress internals: you should make a separate question with the appropriate tags.