How to display decimals as fractions?

Turns out there's a plugin for that. Typography, by nystudio107.

https://nystudio107.com/docs/typogrify/#using-typogrify

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I was never able to get this working with typogrify. It never treated a period immediately surrounded by numbers as a decimal point.

It did inspire me to write a plugin, Fractionalize, to provide a '|fractionalize' filter which does the trick.