heading-last-attr-rule

Explicit empty {} as last token means heading has no attributes; earlier {attrs} attach to inline elements

§4.2

Input

= H1 [link](..){.link-class}{}

Output AST

- type: Section
  level: 1
  heading:
    - type: Text
      value: "H1 "
    - type: Link
      kind: external
      href: ..
      children:
        - type: Text
          value: link
      attributes:
        - key: class
          value:
            - link-class