…Just curious, have you ever used any of Perl(5), Python, or Ruby before?

If I had to guess, ‘foo.IO.words’ probably turns ‘foo’ into an IO object of some sort and then reads words. (Whether it reads the whole file into a string and splits that into words, or if it just reads the next word generator/iterator-style is not especially relevant.) An error throws an exception, like it would in Python or Ruby ‘open('dict.txt')’.

Also I kinda doubt that ‘loop over lines and split them into words’ is more readable than ‘.words’ which presumably does exactly what it says on the tin.

A word is probably defined by either \b or UAX #29. (And since IIRC one of the goals of Perl6 is good support for Unicode, \b hopefully uses the word boundary algorithm in that appendix.)