- `.Ref` and `.RelRef` take a reference (the logical filename for a
page, including extension and/or a document fragment ID) and return
a permalink (or relative permalink) to the referenced document.
- If the reference is a page name (such as `about.md`), the page
will be discovered and the permalink will be returned: `/about/`
- If the reference is a page name with a fragment (such as
`about.md#who`), the page will be discovered and used to add the
`page.UniqueID()` to the resulting fragment and permalink:
`/about/#who:deadbeef`.
- If the reference is a fragment and `.*Ref` has been called from
a `Node` or `SiteInfo`, it will be returned as is: `#who`.
- If the reference is a fragment and `.*Ref` has been called from
a `Page`, it will be returned with the page’s unique ID:
`#who:deadbeef`.
- `.*Ref` can be called from either `Node`, `SiteInfo` (e.g.,
`Node.Site`), `Page` objects, or `ShortcodeWithPage` objects in
templates.
- `.*Ref` cannot be used in content, so two shortcodes have been
created to provide the functionality to content: `ref` and `relref`.
These are intended to be used within markup, like `[Who]({{% ref
about.md#who %}})` or `<a href="{{% ref about.md#who %}}">Who</a>`.
- There are also `ref` and `relref` template functions (used to create
the shortcodes) that expect a `Page` or `Node` object and the
reference string (e.g., `{{ relref . "about.md" }}` or `{{
"about.md" | ref . }}`). It actually looks for `.*Ref` as defined on
`Node` or `Page` objects.
- Shortcode handling had to use a *differently unique* wrapper in
`createShortcodePlaceholder` because of the way that the `ref` and
`relref` are intended to be used in content.
