docs: Prepare for new sub tree

See #11925

docs/content/en/functions/safe/HTMLAttr.md

@@ -1,55 +0,0 @@
----
-title: safe.HTMLAttr
-description: Declares the given key/value pair as a safe HTML attribute.
-categories: []
-keywords: []
-action:
-  aliases: [safeHTMLAttr]
-  related:
-    - functions/safe/CSS
-    - functions/safe/HTML
-    - functions/safe/JS
-    - functions/safe/JSStr
-    - functions/safe/URL
-  returnType: template.HTMLAttr
-  signatures: [safe.HTMLAttr INPUT]
-aliases: [/functions/safehtmlattr]
----
-
-Given a site configuration that contains this menu entry:
-
-{{< code-toggle file=hugo >}}
-[[menus.main]]
-  name = "IRC"
-  url = "irc://irc.freenode.net/#golang"
-{{< /code-toggle >}}
-
-Attempting to use the `url` value directly in an attribute:
-
-```go-html-template
-{{ range site.Menus.main }}
-  <a href="{{ .URL }}">{{ .Name }}</a>
-{{ end }}
-```
-
-Will produce:
-
-```html
-<a href="#ZgotmplZ">IRC</a>
-```
-
-`ZgotmplZ` is a special value, inserted by Go's [template/html] package, that indicates that unsafe content reached a CSS or URL context.
-
-To indicate that the HTML attribute is safe:
-
-```go-html-template
-{{ range site.Menus.main }}
-  <a {{ printf "href=%q" .URL | safeHTMLAttr }}>{{ .Name }}</a>
-{{ end }}
-```
-
-{{% note %}}
-As demonstrated above, you must pass the HTML attribute name _and_ value through the function. Applying `safeHTMLAttr` to the attribute value has no effect.
-{{% /note %}}
-
-[template/html]: https://pkg.go.dev/html/template