With beamer, "Missing { inserted." (regression)

[Joseph Wright]

On 18/02/2022 03:12, Vincent Lefevre wrote:
> On 2022-02-17 18:12:10 +0100, Sam Carter wrote:
>> The behaviour changed with the commit https://github.com/josephwright/beamer/commit/87f1646bd2307010701991129e5a900019b1d48c
> 
> Any reason why this has been broken?

Yes. There was an issue with the behaviour of font switches not 
respecting the beamer 'action' concept. Fixing that means altering the 
definition of \text... such that it no longer allows TeX to expand to 
find an open-group token before hitting something non-expandable.

> Even though the behavior was not officially supported, there were
> no errors without the additional braces and this was simpler and
> more easily readable, so that it was probably used in practice.
> I can see that in many of my old .tex files (not all using beamer).

Lamport's book is entirely clear on the supported syntax for sub- and 
superscripts.

Joseph