Cross-window communication

While editing the ru-version, it turned out that it's more natural in some respects.
It avoids the word tag – DOM entities are involved here,
sometimes it's more accurately stated that we're talking about objects,
the possibility of getting error or null with another origin is indicated, and so on.
But both couldn't avoid confusing newcomers' minds by misunderstanding the terms event and its handler in DOM property
or providing unconfirmed information about short syntax not working, etc.
So let's try to combine the best of each of these versions✅