Added advanced use case FAQ

TelegramBots.wiki/_Sidebar.md

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     * [[Database Handling]]
     * [[Bot Testing]]
     * [[Bot Recovery]]
+    * [[Advanced]]
 * [[Changelog]]
     * [[How To Update]]

TelegramBots.wiki/abilities/Advanced.md

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+# Advanced
+This will be more of a FAQ on some important notes before you embark on your next big bot project!
+
+## Default Abilties
+
+It is possible to declare "DEFAULT" abilities that process non-command messages. This is quite close to a reply. If a user says "Hey there" and the default ability is implemented, it will process this input.
+```java
+ /**
+   * This ability has an extra "flag". It needs a photo to activate! This feature is activated by default if there is no /command given.
+   */
+  public Ability sayNiceToPhoto() {
+    return Ability.builder()
+        .name(DEFAULT) // DEFAULT ability is executed if user did not specify a command -> Bot needs to have access to messages (check FatherBot)
+        .flag(PHOTO)
+        .privacy(PUBLIC)
+        .locality(ALL)
+        .input(0)
+        .action(ctx -> silent.send("Daaaaang, what a nice photo!", ctx.chatId()))
+        .build();
+  }
+```
+
+This ability will send a *"Daaaaang, what a nice photo!"* whenever the bot receives a photo. This is one use case where replies and abilities are interchangeable.
+
+## The Global Flag
+However, there is one important note here. This ability without any additional code will not be able to process photos. There is a global flag in AbilityBot that restricts the kind of "updates" it can process.
+To freely process any update given to your bot, make sure to:
+
+```java
+/**
+   * By default, any update that does not have a message will not pass through abilities.
+   * To customize that, you can just override this global flag and make it return true at every update.
+   * This way, the ability flags will be the only ones responsible for checking the update's validity.
+   */
+  @Override
+  public boolean checkGlobalFlags(Update update) {
+    return true;
+  }
+```