How to find out the correct scope (selector)

Added findings from https://discuss.atom.io/t/how-do-you-configure-use-snippets/335/28

Author: pbihler

README.md

@@ -18,7 +18,7 @@ Snippet files can be either `.json` or `.cson`.
     'body': 'console.log(${1:"crash"});$2'
 ```
 
-The outermost keys are the selectors where this snippets should be active.
+The outermost keys are the selectors where this snippets should be active (details below).
 
 The next level of keys are the snippet names.
 
@@ -56,3 +56,50 @@ You can also use multi-line syntax using `"""` for larger templates:
       }
     """
 ```
+
+### Finding out the correct selector (scope) for a snippet
+
+The outmost key of a snippet is the "scope" that you want the descendent snippets to be available in. To determine the scope of a language, do:
+
+* Open a file of the type for which you want to add a snippet
+* Open the Developer Tools (<kbd>Cmd+Alt+I</kbd> on OS X)
+* Switch to the Console tab
+* Focus the source file and execute the _Editor > Log Cursor Scope_ command (<kbd>Cmd+Alt+P</kbd> on OS X)
+
+The first entry in the array that is logged to the Console is the scope for that language.
+
+If you have special characters (like `+`) in the scope, you have to escape them:
+
+```coffee
+.source.c, .source.c\\+\\+, .source.objc, .source.objc\\+\\+':
+  ...
+```
+
+### Multiple snippets for the same scope
+
+Since the `snippets.cson` file describes one single object, snippets for the same selector must be placed within the same key, so that would work:
+
+```coffee
+'.source.gfm': # The selector for "markdown" (.md) files
+  'Preformatted text':
+    'prefix': 'pre'
+    'body': '`$1`'
+
+  'Strikethrough':
+    'prefix': 'strike'
+    'body': '~~$1~~'
+```
+      
+While this apperently not:
+
+```coffee
+'.source.gfm': # This one is used
+  'Preformatted text':
+    'prefix': 'pre'
+    'body': '`$1`'
+
+'.source.gfm': # Second declaration of the same key, ignored
+  'Strikethrough':
+    'prefix': 'strike'
+    'body': '~~$1~~'
+```