[section]=
const id = 'x' + this.index++
const title = capture_line()
const header = title.trim() ? `<h2><a id="${id}" href="#${id}">${interpret(title)}</a></h2>` : ''
const content = capture_until("[section]", true, true)
;`<section>${header}${interpret(content)}</section>`

[h3]=
const id = 'x' + this.index++
`<h3><a id="${id}" href="#${id}">${interpret(capture_line())}</a></h3>`