php给一组指定的关键词添加span标签

php给一组指定的关键词添加span标签，高亮突出显示关键词

// Example use: $spanned = codeWords($string_containing_keywords);
// My site: andrew.dx.am
// Using colour==blue, but different arrays of words and different 
// colours can be added.
function onlyWholeWords(&$value, $key) {
    // Ignores words after // comment delimiters.
    //$value = "/\b(" . $value . ")\b/";    // doesn't handle comments
    //$value = "/^(?:(?!\/\/).)*\K\b(" . $value . ")\b/"; 
    // \K lookbehind alternative is not supported in PHP < 5.2.4, so use:
    $value = "/^((?:(?!\/\/).)*)\b" . $value . "\b/";
}
function addSpan(&$value, $key, $color='blue') {
    $value = "$1<span style='color:$color'>" . $value . "</span>";
}
function codeWords($code) {
    $keywords = array('as', 'break', 'case', 'class', 'continue', 'default', 
        'do', 'elif', 'else', 'elseif', 'for', 'foreach', 'function', 'if', 
        'new', 'null', 'return', 'self', 'switch', 'this', 'to', 'typeof', 
        'until', 'var', 'void', 'while', 'with');
    $keywords2 = $keywords;
    array_walk($keywords, 'onlyWholeWords');
    array_walk($keywords2, 'addSpan', 'blue');
    $code = preg_replace($keywords, $keywords2, $code);
    return $code;
}