Sometimes I think you just have to consider the intent and accept that the language might not be totally unambiguous. I wouldn't have been put off of drawing a line to enclose the 'world' either - if I was submitting.
However, as said before, it will be interesting to see the published solution.
(Magpie subscribers will probably know about the 'plectrum/take your pick' brouhaha - sometimes the setters/markers do expect solvers to understand 'intent'. I thought it was clear in that one what was expected, some others did and some didn't. Much debate. 😄)