Update README.md

README.md

@@ -3,6 +3,9 @@
 # FragNav
 Android library for managing multiple stacks of fragments (e.g., [Bottom Navigation ](https://www.google.com/design/spec/components/bottom-navigation.html), [Navigation Drawer](https://www.google.com/design/spec/patterns/navigation-drawer.html)).  This library does NOT include the UI for bottom tab bar layout.  For that, I recommend either [BottomBar](https://github.com/roughike/BottomBar) (which is the library shown in the demo) or [AHBottomNavigation](https://github.com/aurelhubert/ahbottomnavigation). This library helps maintain order after pushing onto and popping from multiple stacks(tabs). It also helps with switching between desired tabs and clearing the stacks.
 
+## Restrictions
+Fragments are maintained in a stack per Android's guideline https://developer.android.com/guide/navigation/navigation-principles#navigation_state_is_represented_as_a_stack_of_destinations . A lot of questions get asked about how to maintain only one instance of a fragment, or to pull out a fragment in the middle of the stack. That is outside Android navigation guidelines, and also this library. You may want to rethink your UX.
+
 <img src="https://raw.githubusercontent.com/ncapdevi/FragNav/master/FragNavDemo.gif" width="30%" />
 
 ## Donations