I have a small problem with the "definitions" of functional vs. position isomers. You have a few quite simple examples (pentan-2-one vs pentan-3-one vs pentanal), but there are also a few tricky borderline cases.
When we talk about alcohols, for example, we differenciate primary, secondary and tertiary alcohols because they don't show the same reactivity (especially for oxydation, in this case). But propan-1-ol and propan-2-ol is typically used as a position isomerism example.
On the other hand, I found this here:
I tried to find recent, clear, and official (e.g. from IUPAC) definitions of these terms, but without much success. I tried the "blue book" (IUPAC organic chemistry nomenclature) and "gold book" but nothing. Actually, the terms don't even appear. Maybe we should just forget about them?