message: Mention flags are not supported by `Sandbox`
  Fixes
diff: @@ -6,11 +6,11 @@ use crate::{executor, Application, Command, Element, Settings, Subscription};
  /// simpler interface than [`Application`].
  ///
  /// Unlike an [`Application`], a [`Sandbox`] cannot run any asynchronous
  -/// actions. However, both traits are very similar and upgrading from a
  -/// [`Sandbox`] is very straightforward.
  +/// actions or be initialized with some external flags. However, both traits
  +/// are very similar and upgrading from a [`Sandbox`] is very straightforward.
  ///
  /// Therefore, it is recommended to always start by implementing this trait and
  -/// upgrade only once you need to perform asynchronous work.
  +/// upgrade only once necessary.
  ///
  /// [`Application`]: trait.Application.html
  /// [`Sandbox`]: trait.Sandbox.html
  