Guide: complex data types

I'm not happy about the hand-waving around `cmp`, but I'm not sure how to get around it.
Technically speaking, it’s a matter of style, and putting the comma outside the quotes is the prevalent style in British English.<sup>[[1]](https://en.wikipedia.org/wiki/Quotation_mark#Typographical_considerations)</sup> However, Rust documentation seems to generally follow American English (where putting the comma inside the quotes is more common), so putting the comma inside the quotes would be more consistent.

(Sometimes the British style *is* used in America, particularly in linguistic and philosophical works, because it is clearer and less ambiguous.<sup>[[2]](http://www.wilbers.com/FAQPunctuation.htm)</sup>)