Wrap a span around all instances in a string that match a regular expression.

gistfile1.txt

  public static function span_strings($string, $class = null) {
    /* Takes a string, and surrounds anything surrounded by 4 asterisks with
      * a span tag with an optional class name.
      *
      * If a class is specified in the second argument, it will add
      * a class to the span tag. 
    */

    $match_phrase       = "/\*\*([^**]*)\*\*/";
    $replace_string     = '<span'; 
    $replace_string    .= $class ? ' class="' . $class . '">' : '>';
    $replace_string    .= '${1}</span>';
    $new_string         = preg_replace($match_phrase, $replace_string, $string);

    return $new_string;
  }