Drew, your message is actually much harder to read in Thunderbird that the one you replied to. Maybe using a plain text response in such cases would be best? I had no trouble reading Paul's email, but yours was tricky.

On 03/25/2016 02:19 PM, Drew Adams wrote:
> (Please use plain-text for this mailing list from now on. I won't bother trying to convert the formatting this time.)
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>  
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>> IIUC, you _cannot_ use `func-arity' to test whether something
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>> is a subr.
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> Yes, but you can and should use `subrp' for that.
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> Of course you can. But that's irrelevant here. This is about what `subr-arity' does. Its behavior is not the same as `func-arity' for a non-subr. If we are not deprecating `subr-arity' then it is not enough to send users to the doc for `func-arity'.
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>> IOW, I am repeating the same argument I made before, when
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>> I said that `subr-arity' should not be deprecated and
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>> simply replaced by `func-arity'.
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> I understood it as argument against aliasing `subr-arity' to
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> the new function: this can break _existing_ code if it relies
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> on the fact that `subr-arity' signals an error when called with
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> anything, but builtin.
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> Yes. And?
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> The same argument applies to just having its doc string tell users to use `func-arity'. That might not break existing code, but it breaks the doc string. It no longer says what function `subr-arity' does. And it gives the false impression that `func-arity' does the same thing. In fact, `func-arity' does something /different/ if the arg is not a subr.
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>> This is a step backward.  Unless we are really deprecating
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>> and replacing it, we should document `subr-arity' properly,
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>> as before, with the addition of cross-ref to see `func-arity',
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>> stating that it handles any type of function.
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> I personally don't see why we need two functions for this.
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> So, I would deprecate `subr-arity', but keep it around for
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> backward compatibility.
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> I personally feel the opposite - see my argument about not breaking existing code. But if that will be the decision then that's different. So far, there has been no decision to deprecate `subr-arity', AFAIK.
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> On the other hand, I don't really care. All I want is that there
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> is `func-arity' that works for _any_ function. I'm not attached
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> to anything in the patch and as long as `func-arity' works,
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> `func-arity' works for any function. So your want is satisfied.
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> However, obtaining your want at the expense of also breaking a doc string is not right.
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> feel free to change anything.
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> I'm not going to change the broken doc string. But I certainly hope that someone will.
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> When code is improved, if that change entails needing to change the doc, then the doc should be updated appropriately.
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