[ostream.formatted.print] Use \impldef macro.

[mordante]

The text defines implementation-defined behavior, but it doesn't use the appropriate macro. So the text is not available in "Index of implementation-defined behavior".

[JohelEGP]

See #5693 (comment) for how this macro is used.
That comment also appertains to this specific use.
It was rejected back then.

[JohelEGP]

I think this is also similar to #6359 (comment).

[mordante]

Thanks for the links, searching didn't show them. After reading the links I'm still not sure why this is not implementation-defined behavior. The way I read it is "Whether os refers to a terminal capable of displaying Unicode is determined in an implementation-defined manner". Is this the wrong interpretation?

[tkoeppe]

@mordante I think the point is that the macro expands to the words "implementation-defined", and the macro argument is the explanatory text that goes into the index.

You can just build the PDF with your changes and check what you get (both in the text and in the index)!

[jensmaurer]

Specifically, this appearance of the word "implementation-defined" must be replaced by \impldef{text to appear in the index}