code: public static Pattern compilePattern(final String expr) {
          Pattern pattern;
          final int lastChar = expr.length() - 1;
          if (expr.charAt(0) == '/' && expr.charAt(lastChar) == '/') {
              pattern = Pattern.compile(expr.substring(1, lastChar));
          } else {
              pattern = Pattern.compile(Pattern.quote(expr));
          }
          return pattern;
      }
docs: Convert a string to a Pattern object.
  <ul>
  <li>If the host starts and ends with / then it is compiled as a regular expression</li>
  <li>Otherwise the hosts must exactly match</li>
  </ul>
  
  @param expr the expression to compile