To schedule an eclipse of the sun, which involves a number of related events.

First we define the events, and then we create a phrase to schedule them:

"Totality"
At the time when the penumbra appears:
   say "The sunlight dies away to an eerie, brownish penumbra."
At the time when the eclipse begins:
   say "The moon passes across the disc of the sun, plunging the world into darkness.";
   now the Chamber is dark.
At the time when the eclipse ends:
   say "The moon passes away from the sun, and a gloomy penumbral light returns.";
   now the Chamber is lighted.
At the time when normal sunlight returns:
   say "The sun shines once more bright in the sky, not to be eclipsed again on this spot for another thirty-seven years."
To schedule an eclipse for (totality - a time):
   the penumbra appears at two minutes before totality;
   the eclipse begins at totality;
   the eclipse ends at three minutes after totality;
   normal sunlight returns at five minutes after totality.

Now we make use of the new phrase:

When play begins, schedule an eclipse for 3:27 PM.
The Chamber is a room.
The time of day is 3:25 PM.
Test me with "z / z / z / z / z / z / z / z / z".
Test me with "z / z / z / z / z / z / z / z / z".
Chamber

>(Testing.)

>[1] z
Time passes.

The sunlight dies away to an eerie, brownish penumbra.

>[2] z
Time passes.

>[3] z
Time passes.

The moon passes across the disc of the sun, plunging the world into darkness.

It is now pitch dark in here!

>[4] z
Time passes.

>[5] z
Time passes.

>[6] z
Time passes.

The moon passes away from the sun, and a gloomy penumbral light returns.

Chamber

>[7] z
Time passes.

>[8] z
Time passes.

The sun shines once more bright in the sky, not to be eclipsed again on this spot for another thirty-seven years.

>[9] z
Time passes.

We shall see much more about creating phrases later. Their advantage is that they enable a complicated sequence of operations to be given a meaningful name, and that they can be re-used many times as needed.