Math spacing

From ConTeXt wiki

TeX handles math spacing by breaking a formula into parts, and assigning each of those parts a role such as 'Ord' (a variable or number) or 'Rel' (equality, larger than, et cetera). For each combination of roles, it then looks up the spacing appropriate between them in a table. These are the roles:

Ord e.g. 4 or a or x2
Op Unary operators such as sin or ln.
Bin Binary operators such as '+'
Rel Relationships such as '=' or '>' or '\implies'
Open open brackets of any kind
Close closing brackets of any kind
Punct Punctuation: digit separators like '.' or ','.
Inner Fractions are inner. What else is inner?

To set up e.g. the spacing between ordinal items, do as follows[since 2012]:

\startsetups math:morespacing
    \ordordspacing\textstyle 1mu plus .5mu minus .25mu\relax