[NTG-context] Ignored spacings are ignored

[Henri Menke]

Dear list,

Sorry for the stupid title, I couldn't resist. :-)

LuaTeX has the option to adjust spacing between different classes of
math atoms.  However, looking in the TeXbook, page 170, in the table for
spacings between adjacent atoms, we find that some of those spacing are
undefined (* in the table) and therefore, when TeX encounters this
combination, spacing is just skipped.

This also translates to the parameters in LuaTeX.  For example the
combination Open-Bin is skipped by TeX and therefore setting the
corresponding parameter just does nothing.

\Umathordrelspacing\textstyle=50mu
\Umathopenbinspacing\textstyle=50mu
$a = (-2)$
\bye

So my question is, what is the point of the parameters that describe
these skipped combinations?  Shouldn't they just be deleted?
Alternatively, they could actually be implemented to do something.

More context: https://tex.stackexchange.com/questions/532758

Kind regards,
Henri