note:
  ┌─ test.html:1:1
  │
1 │ this is a tag: <h1>test</h1>
  │                 ^^       ^^ end tag
  │                 │
  │                 start tag
2 │
3 │ tags can have attributes: <div id = foobar>
  │                                ^^   ^^^^^^ attr value
  │                                │
  │                                attr name
4 │
5 │ Attribute values can be quoted: <input name = 'age' type = "number">
  │                                        ^^^^   ^^^   ^^^^   ^^^^^^ attr value
  │                                        │      │     │
  │                                        │      │     attr name
  │                                        │      attr value
  │                                        attr name