bug#13823: 24.3.50; Elisp manual description of property `pure'

[Drew Adams]

> If you can come up with a good description of what
> it does, I'm all ears.

You presumably know the content to be communicated - just what effect property
`put' has, when to use it, any gotchas or other things to be aware of etc.

I do not really know.  I'm asking for precisely that info.

If you tell me the content - what `put' does, I will be more than glad to offer
help with the wording.


>From the bug #13052 thread, it seems that this might be the effect and 
>condition
of use, but please correct if wrong:

 Non-nil means that when the symbol's function is
 called with only constant arguments the byte-compiler
 evaluates the call and replaces it in the compiled
 code by its value.[*]

 This is similar to replacing a macro call by the
 evaluation of its expansion.

 Use `put' only when the function has no side effects
 and every evaluation of that function call returns
 the same value regardless of the evaluation context.

[*] Does the byte-compiler always do this when the condition is satisfied?  Or
does non-nil `pure' mean only that it might do this?


Is the above description correct?  Should something else be said?

Perhaps the condition is too strong?  Is there a use case for a function that
might not give the same result in all contexts, but for which the only
relevant/intended context is byte-compilation?