What requires a DIP?

[Quirin Schroll]

I’ve been told by randoms a couple of times now that some 
proposed change, which I considered a minor enhancement, needs a 
DIP. How do people determine that? What are the “official” rules 
on what needs a DIP and what doesn’t? As far as I see, there 
aren’t any.

My sense was that, informally:
* Any change that necessitates potentially real-world breakage 
needs a DIP.
* Mere additions need a DIP if they introduce a new language 
feature.
* Even small additions need a DIP if they require justification 
in terms of cost–benefit ratio, with cost both in terms of 
initial implementation and long-term maintenance.

What doesn’t fit those criteria, are additions that give The 
Obvious Meaning™ to something that is currently an error and has 
obvious benefits for little implementation cost and essentially 
no additional maintenance cost.