code: function formatSubPath (path) {
    const trimmed = path.trim();
    // invalid leading 0
    if (path.charAt(0) === '0' && isNaN(path)) { return false }
  
    return isLiteral(trimmed) ? stripQuotes(trimmed) : '*' + trimmed
  }
docs: Format a subPath, return its plain form if it is
  a literal string or number. Otherwise prepend the
  dynamic indicator (*).