Dr S Bhatia

This cannot be successfully achieved as yet in moodle.

first everyone clamours for making activities restrictions so that every tom dicken or harry dropping in by the website can't do it.

Now you want them to do it.

workaround is, if you want guests to take a quiz, put that quiz's  questions in a lesson. lessons can be taken by the guests.
so have both- a 'quiz' and a lesson called 'quiz for guests'. former will be taken by only the enrolled people and latter only by guests. (put a warning that enrolled people need not take this or something )

Import it to moodle and then export it in Moodle it is exported as

::Which are capitals:::Which are capitals:{
=Paris
~Belgium
~Olaf
=London
}

In the documantation it is clearly written that if you dont specify a question name, the entire question would be taken as a question name. That's why if u export it after importing from gift and have given no name to the question, moodle is still looking for a colon demarkated name and christens the whole question as nquestion name.

WORKAROUND: in the giftmaker, a default question name should always be present. e.g. 'question' or 'Q' or something which even if left unedited, causes no harm. this way, moodle will get a question name and will stop interpreting other colons.

flipside: if you are not fond of naming your questions, then all questions will appear as 'Q' or 'Question' in your list.

FUNNY part: The terminal end of your digestive system has something called a colon. Being a doctor it took me a few moments to bring my thinking from that colon to this colon.

An empty line may confuse some students and they may think thayt the question is not working properly.

see this picture

so instead, write somwthing there like 'blank' or 'empty field' or something appropriate

turn editing on.
you'll see a 'add block' block