// 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;
}