Would it make sense to remove the link from the printed text and instead add a new line followed by whatever `check_package (fcn, "io")` would return?
That way a user would get notified if they already have the io package installed but not loaded.

That could read something like:

Functions for XML I/O are provided in the io package.
The 'xmlread' function belongs to the io package from Octave Forge
which you have installed but not loaded.  To load the package, run 'pkg
load io' from the Octave prompt.

That is not entirely correct because `xmlread` should belong to Octave core. But it still contains useful information...

Maybe, we could use "is part of" instead of "belongs to" in that sentence. Is that valid English? And would it be "more correct" in all cases?

In that case, we could probably also omit the introductory sentence.
What do you think?

@Nick: It seems that the attached file is missing

yes I had seen that and had actually saved it from previous versions when I was curious about what 'old' matlab functions might still be unimplemented, but never got as far as writing a comparison script and wasn't sure where to pull an octave manifest from for comparison, and then similarly a manifest for packages (forge hosted packages can probably be pulled from the octave forge site pages, now that I believe that's being updated again when packages are released.)

Yes, I think it makes sense to add special case entries for any function in core Matlab that is in some Octave package but not yet in core Octave that point users to the package.

It would be great if we could automate the job of updating the lists of unimplemented functions but I don't know how we could always do it reliably.  It depends on what functions are in Matlab and its toolboxes as well as the functions in Octave and its packages.  As far as I know, that has always been edited by hand.

just noticed:

>> help xmlread
error: help: The 'xmlread' function is not yet implemented in Octav
e.

Please read <https://www.octave.org/missing.html> to learn how you
can
contribute missing functionality.

>> pkg load io

>> help xmlread
'xmlread' is a function from the file C:\Programs\Octave\octave-6.3
.0-w64\mingw64\share\octave\packages\io-2.6.3\xmlread.m
...
 -- Function File: NODE = xmlread (FNAME)

i know there were some recent crash related bugs that forced temporary removal of xmlread from io, but with it back now i'm assuming the 'missing function' should be changed to a 'part of package that is installed but not loaded' message.  i'm not familiar with where those things reside to throw a patch together to do that.