{{ $page := . }}

{{ $result := $page.Content }}

{{ $matches := findRESubmatch "<h([1-6])[ >]" $result }}

{{ with $matches }}
    {{ $max := 0 }}

    {{ range . }}
        {{ $level := index . 1 | int }}

        {{ if gt $level $max }}
            {{ $max = $level }}
        {{ end }}
    {{ end }}

    {{ if and $max (lt $max 6) }}
        {{ $shift := sub 6 $max }}

        {{ range seq $max | collections.Reverse }}
            {{ $old := . }}
            {{ $new := add $old $shift }}

            {{ $result = replaceRE (printf "<h%d([ >])" $old) (printf "<h%d$1" $new) $result }}
            {{ $result = replaceRE (printf "</h%d>" $old) (printf "</h%d>" $new) $result }}
        {{ end }}
    {{ end }}
{{ end }}

{{ return $result }}