» I think that your "textual digits" only arise in the absence of proper
» markup, just as it is common to have other symbols sprayed into the text,
» in the absence of a proper symbol environments.

of course not. §~2.3 has nothing to do with maths, neither p.~12312.

Up to some extent, I personnally consider that _units_ are not maths
(you can write : I drive my car 3 miles or 12 km; this is text, it
would get italised if the context tells so, etc.) The \textmu in µm is
also a textual object. (I would use \text{\normalfont  µm} in a math
equation).

Thierry Bouche
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« Ils vivent pour vivre, et nous, hélas ! nous vivons pour savoir. »
Charles Baudelaire, Paris.