docs: static void checkIdentifier(final String name, final int start,
              final int end, final String msg) {
          if (name == null || (end == -1 ? name.length() <= start : end <= start)) {
              throw new IllegalArgumentException("Invalid " + msg
                      + " (must not be null or empty)");
          }
          if (!Character.isJavaIdentifierStart(name.charAt(start))) {
              throw new IllegalArgumentException("Invalid " + msg
                      + " (must be a valid Java identifier): " + name);
          }
          int max = end == -1 ? name.length() : end;
          for (int i = start + 1; i < max; ++i) {
              if (!Character.isJavaIdentifierPart(name.charAt(i))) {
                  throw new IllegalArgumentException("Invalid " + msg
                          + " (must be a valid Java identifier): " + name);
              }
          }
      }