There is no API call that will just return a list of page names
DebConf18/DayTrip/Registration/A
DebConf18/DayTrip/Registration/B
DebConf18/DayTrip/Registration/C
like one sees in
https://wiki.debconf.org/wiki/Special:PrefixIndex/DebConf18/DayTrip/Registr…
without insisting on adding
pageid="7823" ns="0" to the result
even if one uses prop=info & ininfo=...
nor just printing it in the above plain text format without
any other junk added, even if one uses format=txt.
The best one can do is
wget -O z
"https://wiki.debconf.org/api.php?action=query&generator=allpages&gapprefix=DebConf18/DayTrip/Registration&gaplimit=22&format=txt"
perl -wnle 'print for m!DebConf18/DayTrip/Registration.+!g;' z
DebConf18/DayTrip/Registration/A
DebConf18/DayTrip/Registration/B
DebConf18/DayTrip/Registration/C