Using deep data merge (post tag is inherited from posts/posts.json) and updates to use 0.7.0.

posts/firstpost.md

@@ -1,8 +1,8 @@
 ---
 title: This is my first post.
+description: This is a post on My Blog about agile frameworks.
 date: 2018-05-01
 tags:
-  - post
   - another-tag
 layout: layouts/post.njk
 ---

posts/fourthpost.md

@@ -1,5 +1,6 @@
 ---
 title: This is my fourth post.
+description: This is a post on My Blog about touchpoints and circling wagons.
 date: 2018-09-30
 tags: second-tag
 layout: layouts/post.njk

posts/posts.json

@@ -0,0 +1,5 @@
+{
+  "tags": [
+    "posts"
+  ]
+}

posts/secondpost.md

@@ -1,8 +1,8 @@
 ---
 title: This is my second post.
+description: This is a post on My Blog about leveraging agile frameworks.
 date: 2018-07-04
 tags:
-  - post
   - number-2
 layout: layouts/post.njk
 ---

posts/thirdpost.md

@@ -1,8 +1,8 @@
 ---
 title: This is my third post.
+description: This is a post on My Blog about win-win survival strategies.
 date: 2018-08-24
 tags:
-  - post
   - second-tag
 layout: layouts/post.njk
 ---