`sig
type heading = [ `H1 | `H2 | `H3 | `H4 | `H5 | `H6 ]
type block = [ `Address | `Blockquote | `Div | `P | `Pre ]
type inline =
[ `Abbr
| `Acronym
| `Br
| `Cite
| `Code
| `Dfn
| `Em
| `Kbd
| `Q
| `Samp
| `Span
| `Strong
| `Var ]
type flow =
[ `Abbr
| `Acronym
| `Address
| `Blockquote
| `Br
| `Cite
| `Code
| `Dfn
| `Div
| `Em
| `H1
| `H2
| `H3
| `H4
| `H5
| `H6
| `Kbd
| `P
| `Pre
| `Q
| `Samp
| `Span
| `Strong
| `Var ]
end`