Not pure HTML, actually a template. This doesn't parse fully. And even if, it requires N:M mapping.

This mapping is unfinished: 5 of 115 nodes are still unmarked.

Code view:

A painting is a person's account of this edit as text, recorded independently of the node mapping - a rendering often has several equally defensible answers where the mapping has one. Deletions and insertions carry no position on the opposite side in a painting, so that panel draws no caret for them.

Before

1<h{{ .Level }} id="{{ .Anchor | safeURL }}">{{ .Text | safeHTML }}
2{{- if and (ge .Level .Page.Site.Params.anchors.min) (le .Level .Page.Site.Params.anchors.max) }}{{" " -}}
3<a class="anchor-link" href="#{{ .Anchor | safeURL }}" aria-label="Link to this section: {{ .Text | safeHTML }}"></a>
4{{- end -}}
5</h{{ .Level }}>
6

After

1{{- $id := .Anchor | safeURL -}}
2{{- $text := .Text | safeHTML -}}
3<h{{ .Level }} id="{{ $id }}">{{ $text }}
4{{- if and (ge .Level .Page.Site.Params.anchors.min) (le .Level .Page.Site.Params.anchors.max) }}{{" " -}}
5<a class="anchor-link" href="#{{ $id }}" aria-label="Link to this section: {{ $text }}"></a>
6{{- end -}}
7</h{{ .Level }}>
8

Before

document
element
start_tag
< "<"
tag_name "h"
attribute
attribute_name "{{"
attribute
attribute_name ".Level"
attribute
attribute_name "}}"
attribute
attribute_name "id"
= "="
quoted_attribute_value
" "\""
attribute_value "{{ .Anchor | safeURL }}"
" "\""
> ">"
text "{{ .Text | safeHTML }}\n{{- if and (ge .Level .Page.Site.Para"...
element
start_tag
< "<"
tag_name "a"
attribute
attribute_name "class"
= "="
quoted_attribute_value
" "\""
attribute_value "anchor-link"
" "\""
attribute
attribute_name "href"
= "="
quoted_attribute_value
" "\""
attribute_value "#{{ .Anchor | safeURL }}"
" "\""
attribute
attribute_name "aria-label"
= "="
quoted_attribute_value
" "\""
attribute_value "Link to this section: {{ .Text | safeHTML }}"
" "\""
> ">"
end_tag
</ "</"
tag_name "a"
> ">"
text "{{- end -}}"
end_tag
</ "</"
tag_name "h"
ERROR
ERROR "{{ .Level }}"
> ">"

After

document
text "{{- $id := .Anchor | safeURL -}}\n{{- $text := .Text | safeHT"...
element
start_tag
< "<"
tag_name "h"
attribute
attribute_name "{{"
attribute
attribute_name ".Level"
attribute
attribute_name "}}"
attribute
attribute_name "id"
= "="
quoted_attribute_value
" "\""
attribute_value "{{ $id }}"
" "\""
> ">"
text "{{ $text }}\n{{- if and (ge .Level .Page.Site.Params.anchors."...
element
start_tag
< "<"
tag_name "a"
attribute
attribute_name "class"
= "="
quoted_attribute_value
" "\""
attribute_value "anchor-link"
" "\""
attribute
attribute_name "href"
= "="
quoted_attribute_value
" "\""
attribute_value "#{{ $id }}"
" "\""
attribute
attribute_name "aria-label"
= "="
quoted_attribute_value
" "\""
attribute_value "Link to this section: {{ $text }}"
" "\""
> ">"
end_tag
</ "</"
tag_name "a"
> ">"
text "{{- end -}}"
end_tag
</ "</"
tag_name "h"
ERROR
ERROR "{{ .Level }}"
> ">"