Determine if container or window is focusable

I want to find out if a container contains any focusable objects. I couldn't find a property or function that provides that information.

The following code I copied from Layout.focus() works for me:

from prompt_toolkit.layout.layout import walk
from prompt_toolkit.layout.containers import Window, to_container

def is_focusable(container):
    for c in walk(to_container(container), skip_hidden=True):
        if isinstance(c, Window) and c.content.is_focusable():
            return True
    return False

Would this be a good addition for the Container class?

@property
def is_focusable(self):
    for c in walk(self, skip_hidden=True):
        if isinstance(c, Window) and c.content.is_focusable():
            return True
    return False

I can live with my solution, but I think this should be provided out of the box.

Start with Layout.focus() and the existing walk(), Window, and to_container() references in prompt_toolkit.layout.layout and prompt_toolkit.layout.containers. Determine whether the proposed Container-level property fits the existing API, then verify that it reports whether any visible Window content is focusable.