These functions ask a question and parse a response from the user.
They return true if the answer is affirmative,
or false if the answer is negative.
y-or-n-p is for asking the user a question whose answer is either
"yes" or "no."
It is intended that the reply require
the user to answer a yes-or-no question with a single
character.
yes-or-no-p is also for asking the user a question
whose answer is either "Yes" or "No."
It is intended that the reply require
the user to take more action than just a single keystroke, such as typing
the full word yes or no followed by a newline.
y-or-n-p types out a message (if supplied), reads an answer
in some implementation-dependent manner (intended to be short and simple,
such as reading a single character such as Y or N).
yes-or-no-p types out a message (if supplied),
attracts the user's attention (for example, by ringing
the terminal's bell),
and reads an answer
in some implementation-dependent manner (intended to be multiple characters,
such as YES or NO).
If format-control is supplied and not nil,
then a fresh-line operation is performed; then
a message is printed as if format-control and arguments
were given to format.
In any case, yes-or-no-p and y-or-n-p will provide
a prompt such as "(Y or N)" or "(Yes or No)" if appropriate.
All input and output are performed using query I/O.