eqn(7): Primes, opprime, and '

["Anthony J. Bentley" <anthony@anjbe.name>]

Hi,

https://www.w3.org/TR/MathML3/chapter7.html#chars.pseudo-scripts says:

   "...the preferred encoding of 'x prime' is
      <msup><mi>x</mi><mo>&#x2032;<!--PRIME--><!--PRIME--></mo></msup>
    and not
      <mi>x'</mi>
    or any other variants not using an explicit script construct."

Superscripting primes this way is common in typesetting. In TeX,
' is equivalent to ^{\prime}:
https://tex.stackexchange.com/questions/87134/

The OpenGL manuals typically use "sup prime", as in gluProject(3):

    v sup prime ~=~ P ~times~ M ~times~ v

GNU eqn(1) has the opprime keyword:

   e opprime
      This is a variant of prime that acts as an operator on e.  It
      produces a different result from prime in a case such as
      A opprime sub 1: with opprime the 1 is tucked under the prime as
      a subscript to the A (as is conventional in mathematical
      typesetting), whereas with prime the 1 is a subscript to the
      prime character.  The precedence of opprime is the same as that
      of bar and under, which is higher than that of everything except
      accent and uaccent.  In unquoted text a ' that is not the first
      character is treated like opprime.

So it appears that in groff(1) ' and opprime are equivalent to
(essentially) sup prime.

It's, um, hard to grep manuals for this usage, but I can believe that
people would use ' this way, both because it's documented in groff and
because they would expect it to work as TeX. So mandoc(1) having
opprime, and ' equivalent to opprime, would be nice.

-- 
Anthony J. Bentley
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