function substr(str, start, len) {
  //  discuss at: http://phpjs.org/functions/substr/
  //     version: 909.322
  // original by: Martijn Wieringa
  // bugfixed by: T.Wild
  // improved by: Onno Marsman
  // improved by: Brett Zamir (http://brett-zamir.me)
  //  revised by: Theriault
  //        note: Handles rare Unicode characters if 'unicode.semantics' ini (PHP6) is set to 'on'
  //   example 1: substr('abcdef', 0, -1);
  //   returns 1: 'abcde'
  //   example 2: substr(2, 0, -6);
  //   returns 2: false
  //   example 3: ini_set('unicode.semantics',  'on');
  //   example 3: substr('a\uD801\uDC00', 0, -1);
  //   returns 3: 'a'
  //   example 4: ini_set('unicode.semantics',  'on');
  //   example 4: substr('a\uD801\uDC00', 0, 2);
  //   returns 4: 'a\uD801\uDC00'
  //   example 5: ini_set('unicode.semantics',  'on');
  //   example 5: substr('a\uD801\uDC00', -1, 1);
  //   returns 5: '\uD801\uDC00'
  //   example 6: ini_set('unicode.semantics',  'on');
  //   example 6: substr('a\uD801\uDC00z\uD801\uDC00', -3, 2);
  //   returns 6: '\uD801\uDC00z'
  //   example 7: ini_set('unicode.semantics',  'on');
  //   example 7: substr('a\uD801\uDC00z\uD801\uDC00', -3, -1)
  //   returns 7: '\uD801\uDC00z'

  var i = 0,
    allBMP = true,
    es = 0,
    el = 0,
    se = 0,
    ret = '';
  str += '';
  var end = str.length;

  // BEGIN REDUNDANT
  this.php_js = this.php_js || {};
  this.php_js.ini = this.php_js.ini || {};
  // END REDUNDANT
  switch ((this.php_js.ini['unicode.semantics'] && this.php_js.ini['unicode.semantics'].local_value.toLowerCase())) {
    case 'on':
      // Full-blown Unicode including non-Basic-Multilingual-Plane characters
      // strlen()
      for (i = 0; i < str.length; i++) {
        if (/[\uD800-\uDBFF]/.test(str.charAt(i)) && /[\uDC00-\uDFFF]/.test(str.charAt(i + 1))) {
          allBMP = false;
          break;
        }
      }

      if (!allBMP) {
        if (start < 0) {
          for (i = end - 1, es = (start += end); i >= es; i--) {
            if (/[\uDC00-\uDFFF]/.test(str.charAt(i)) && /[\uD800-\uDBFF]/.test(str.charAt(i - 1))) {
              start--;
              es--;
            }
          }
        } else {
          var surrogatePairs = /[\uD800-\uDBFF][\uDC00-\uDFFF]/g;
          while ((surrogatePairs.exec(str)) != null) {
            var li = surrogatePairs.lastIndex;
            if (li - 2 < start) {
              start++;
            } else {
              break;
            }
          }
        }

        if (start >= end || start < 0) {
          return false;
        }
        if (len < 0) {
          for (i = end - 1, el = (end += len); i >= el; i--) {
            if (/[\uDC00-\uDFFF]/.test(str.charAt(i)) && /[\uD800-\uDBFF]/.test(str.charAt(i - 1))) {
              end--;
              el--;
            }
          }
          if (start > end) {
            return false;
          }
          return str.slice(start, end);
        } else {
          se = start + len;
          for (i = start; i < se; i++) {
            ret += str.charAt(i);
            if (/[\uD800-\uDBFF]/.test(str.charAt(i)) && /[\uDC00-\uDFFF]/.test(str.charAt(i + 1))) {
              se++; // Go one further, since one of the "characters" is part of a surrogate pair
            }
          }
          return ret;
        }
        break;
      }
      // Fall-through
    case 'off':
      // assumes there are no non-BMP characters;
      //    if there may be such characters, then it is best to turn it on (critical in true XHTML/XML)
    default:
      if (start < 0) {
        start += end;
      }
      end = typeof len === 'undefined' ? end : (len < 0 ? len + end : len + start);
      // PHP returns false if start does not fall within the string.
  }
  return undefined; // Please Netbeans
}
      // PHP returns false if the calculated end comes before the calculated start.
      // PHP returns an empty string if start and end are the same.
      // Otherwise, PHP returns the portion of the string from start to end.
      return start >= str.length || start < 0 || start > end ? !1 : str.slice(start, end);