And in the same context, would you please be so kind as to elaborate following difference:

$kernel->yield( 'keepalive', $_[HEAP]{client} );
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is used to address the ReadWrite instance.

In the sub "on_connect_error" (see first post) following code is used to delete the wheel upon an error:

delete $_[HEAP]{client}{$wheel_id};
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I don't understand the difference between these two. Still struggling with a lot aspects in POE and I appreciate each input.

I think the first one is a typo. It refers to the hash of all clients rather than a particular client. It should probably be

$kernel->yield('keepalive', $_[HEAP]{client}{$wheel_id});
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