🪦 (nonphatic@cybre.space)'s status on Thursday, 14-Apr-2022 06:17:16 UTC

so the SGML handbook was published I think in 1990, a few years after the release of ISO 8879:1988, which it wholly contains
the text Markup of Mathematical Formulas was published in 1989, while its precursor Electronic Preparation and Markup was published in 1988 (which uses SGML)
there's new symbols in TR 9573-13:1991, and based on the years, I think it's entirely possible that the timeline went like this:
* 1988: SGML is released
* 1988: EPM is published
* 1989: MMF is published
* 1990: SGML handbook is published, containing the entire SGML spec, including an entity set missing ⍼
* 1991: TR 9573-13 is released, adding ⍼ sourced from MMF (?) or EPM (?)
I then just need access to either MMF and EPM to check