note:
  ┌─ test.html:3:17
  │
3 │ Here is a tag: <strong >very cool</strong>
  │                 ^^^^^^             ^^^^^^ EndTag
  │                 │
  │                 StartTag
4 │
5 │ Tags can have attributes: <div id = foo >...</div>
  │                                ^^   ^^^ attribute value
  │                                │
  │                                attribute name
6 │
7 │ Attribute values can be quoted: <input name = 'age' type = "number">
  │                                                ^^^          ^^^^^^ in double quotes
  │                                                │
  │                                                in single quotes