Add YAML Is A Superset Of JSON as a YAML til

yaml/yaml-is-a-superset-of-json.md

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+# YAML Is A Superset Of JSON
+
+Put another way, JSON is a subset of YAML.
+
+Here is what the YAML spec has to say:
+
+> YAML can therefore be viewed as a natural superset of JSON, offering improved
+> human readability and a more complete information model. This is also the
+> case in practice; every JSON file is also a valid YAML file.
+
+We can _see_ this in practice by using our favorite YAML parse to read a JSON
+file. For me that is Ruby and its built-in YAML library.
+
+First, consider the following JSON file (`data.json`):
+
+```json
+{
+  "data": [
+    "one",
+    "two",
+    "three"
+  ],
+  "number": 22
+}
+```
+
+Now, I'll open up an IRB session (Ruby's interactive REPL) and read it in.
+
+```ruby
+> require 'yaml'
+=> true
+> YAML.load_file('data.json')
+=> {"data"=>["one", "two", "three"], "number"=>22}
+```
+
+It works. And for me, having not considered those two format related, this
+isn't something I would have expected to work.
+
+[source](http://yaml.org/spec/1.2/spec.html#id2759572)