function scanFlag(path) {
  const { index, pathValue } = path;
  const code = pathValue.charCodeAt(index);

  if (code === 0x30/* 0 */) {
    path.param = 0;
    path.index += 1;
    return;
  }

  if (code === 0x31/* 1 */) {
    path.param = 1;
    path.index += 1;
    return;
  }

  path.err = `${error}: invalid Arc flag "${pathValue[index]}", expecting 0 or 1 at index ${index}`;
}
Validates an A (arc-to) specific path command value.
Usually a `large-arc-flag` or `sweep-flag`.

@param {SVGPath.PathParser} path the `PathParser` instance