Add headless bundle documentation

Also update the leaf bundle section; mention that they can be directly under
content/ directory too.

content/content-management/front-matter.md

@@ -103,6 +103,9 @@ There are a few predefined variables that Hugo is aware of. See [Page Variables]
 `expiryDate`
 : the datetime at which the content should no longer be published by Hugo; expired content will not be rendered unless the `--buildExpired` flag is passed to the `hugo` command.
 
+`headless`
+: if `true`, sets a leaf bundle to be [headless][headless-bundle].
+
 `isCJKLanguage`
 : if `true`, Hugo will explicitly treat the content as a CJK language; both `.Summary` and `.WordCount` work properly in CJK languages.
 
@@ -189,6 +192,7 @@ It's possible to set some options for Markdown rendering in a content's front ma
 [content type]: /content-management/types/
 [contentorg]: /content-management/organization/
 [definetype]: /content-management/types/#defining-a-content-type "Learn how to specify a type and a layout in a content's front matter"
+[headless-bundle]: /content-management/page-bundles/#headless-bundle
 [json]: https://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf "Specification for JSON, JavaScript Object Notation"
 [lists]: /templates/lists/#ordering-content "See how to order content in list pages; for example, templates that look to specific _index.md for content and front matter."
 [lookup]: /templates/lookup-order/ "Hugo traverses your templates in a specific order when rendering content to allow for DRYer templating."

content/content-management/page-bundles.md

@@ -2,7 +2,7 @@
 title : "Page Bundles"
 description : "Content organization using Page Bundles"
 date : 2018-01-24T13:09:00-05:00
-lastmod : 2018-01-26T10:58:36-05:00
+lastmod : 2018-01-28T22:26:40-05:00
 linktitle : "Page Bundles"
 keywords : ["page", "bundle", "leaf", "branch"]
 categories : ["content management", "bundle"]
@@ -30,12 +30,13 @@ A Page Bundle can be one of two types:
 | Usage           | Collection of content and attachments for single pages | Collection of content and attachments for section pages |
 | Index file name | `index.md` [^fn:1]                                     | `_index.md` [^fn:1]                                     |
 | Layout type     | `single`                                               | `list`                                                  |
+| Nesting         | Doesn't allow nesting of more bundles under it         | Allows nesting of leaf/branch bundles under it          |
 | Example         | `content/posts/my-post/index.md`                       | `content/posts/_index.md`                               |
 
 
 ## Leaf Bundles {#leaf-bundles}
 
-A _Leaf Bundle_ is a directory at any hierarchy within a [Section](/content-management/sections/)
+A _Leaf Bundle_ is a directory at any hierarchy within the `content/`
 directory, that contains at least an **`index.md`** file.
 
 {{% note %}}
@@ -50,6 +51,8 @@ get exotic, you can define your own media type.
 
 ```text
 content/
+├── about
+│   ├── index.md
 ├── posts
 │   ├── my-post
 │   │   ├── content1.md
@@ -68,9 +71,13 @@ content/
             └── index.md
 ```
 
-In the above example `content/` directory, there are three leaf
+In the above example `content/` directory, there are four leaf
 bundles:
 
+about
+: This leaf bundle is at the root level (directly under
+    `content` directory) and has only the `index.md`.
+
 my-post
 : This leaf bundle has the `index.md`, two other content
     Markdown files and two image files.
@@ -84,14 +91,45 @@ another-leaf-bundle
 
 {{% note %}}
 The hierarchy depth at which a leaf bundle is created does not matter,
-as long as (1) it's not inside another **leaf** bundle (2) it's not
-directly under the `content/` directory.
+as long as it is not inside another **leaf** bundle.
 {{% /note %}}
 
 
-### Headless Leaf Bundle {#headless-leaf-bundle}
+### Headless Bundle {#headless-bundle}
 
-**TODO**
+A headless bundle is a bundle that is configured to not get published
+anywhere:
+
+-   It will have no `Permalink` and no rendered HTML in `public/`.
+-   It will not be part of `.Site.RegularPages`, etc.
+
+But you can get it by `.Site.GetPage`. Here is an example:
+
+```html
+{{ $headless := .Site.GetPage "page" "some-headless-bundle" }}
+{{ $reusablePages := $headless.Resources.Match "author*" }}
+<h2>Authors</h2>
+{{ range $reusablePages }}
+    <h3>{{ .Title }}</h3>
+    {{ .Content }}
+{{ end }}
+```
+
+A leaf bundle can be made headless by adding below in the Front Matter
+(in the `index.md`):
+
+```toml
+headless = true
+```
+
+{{% note %}}
+Only leaf bundles can be made headless.
+{{% /note %}}
+
+There are many use cases of such headless page bundles:
+
+-   Shared media galleries
+-   Reusable page content "snippets"
 
 
 ## Branch Bundles {#branch-bundles}
@@ -137,7 +175,8 @@ bundles (and a leaf bundle):
     nested leaf bundle.
 
 {{% note %}}
-The hierarchy depth at which a branch bundle is created does not matter.
+The hierarchy depth at which a branch bundle is created does not
+matter.
 {{% /note %}}
 
 [^fn:1]: The `.md` extension is just an example. The extension can be `.html`, `.json` or any of any valid MIME type.