docs: itemkind behavior and filtering warning, also extend examples.

README.md

@@ -86,6 +86,14 @@ A lisp program to decide on a per item basis if it should be included in
 the playlist, return `nil` to not include items, return any other value
 to include them.
 
+**!!! The filter expression will include all items matching, if you do
+not specify the kind of item to include/exclude all of them will be
+added. Should you allow a playlist to be included all of it's items
+will be added to the generated playlist !!!**
+
+It's best to be explicit and always specify the item kinds you want to
+include: `(and (or (is-type "MusicAlbum") (is-type "Audio")) . rest of filter)`.
+
 The configuration page defines some useful functions to make it easier
 to create filters. The above filter for liked items could be simplified
 to: `(is-favourite)`.

examples.md

@@ -1,10 +1,27 @@
 # Examples
 
-* `Favourite Pop`: A Playlist
+- `Favourite Pop`: A playlist
   containing all favourite items of the genre pop.
   ```
   Id: Favourite Pop
   Name: Favourite Pop
   Program: |
-    (and (is-favorite) (is-genre "pop" (genre-list)))
+    (and (is-type "Audio") (is-favorite) (is-genre "pop" (genre-list)))
+  ```
+- `Electro Swing`: A playlist containing all items
+  which have a genre that contains "electro" and a
+  genre that contains "swing". It will only include
+  albums and single tracks.
+  ```
+  Id: Electro Swing
+  Name: Electro Swing
+  Program: |
+    (let
+      (g (genre-list))
+      (and
+        (or
+          (is-type "Audio")
+          (is-type "MusicAlbum"))
+        (is-genre "electro" g)
+        (is-genre "swing" g)))
   ```