code: private static int checkIndexOf(final String str, final int strStartIndex, final String search) {
          final int endIndex = str.length() - search.length();
          if (endIndex >= strStartIndex) {
              for (int i = strStartIndex; i <= endIndex; i++) {
                  if (checkRegionMatches(str, i, search)) {
                      return i;
                  }
              }
          }
          return -1;
      }
docs: Checks if one string contains another starting at a specific index using the
  case-sensitivity rule.
  <p>
  This method mimics parts of {@link String#indexOf(String, int)}
  but takes case-sensitivity into account.
  
  @param str  the string to check, not null
  @param strStartIndex  the index to start at in str
  @param search  the start to search for, not null
  @return the first index of the search String,
  -1 if no match or {@code null} string input
  @throws NullPointerException if either string is null
  @since 2.0