Fixing issue 21741: Modifying reference documentation

[pat-jpnk]

Fixes #21741

Changing the reference documentation. Fix was first tested in private project, based on the comments contained in runfiles_src.h. Related to comments of issue #11212.

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[fmeum]

Thanks for improving the docs!

@meteorcloudy Is this change safe to merge or does it need disambiguation so that it doesn't apply internally?

[meteorcloudy]

This might be internal specific doc. /cc @comius

[meteorcloudy]

@pzembrod Can you help address this?

[davidben]

@meteorcloudy Is this change safe to merge or does it need disambiguation so that it doesn't apply internally?

FWIW, from the perspective of someone working on a project that needs to straddle both external and internal universes, it would be nice if the patterns could align a bit better. Every divergence is one more bit of friction we have to deal with when updating things.