bug#58727: 29.0.50; rx doc: Semantics of RX...

[Mattias Engdegård]

> The resulting regexps are concatenating like with an implicit `seq'.
> This is not trivial, though: in stringish regexps the repetition
> operators are only unary, and different interpretations would make sense
> for `rx' (implicit `seq', implicit `or').

The rule is implicit concatenation unless specified otherwise; maybe we could 
say that in the leading paragraph. (`or` is the only place where concatenation 
isn't done.)

Otherwise I think we should grant our readers some common sense. It's not a 
formal specification but meant for humans to understand, and I'm quite sure 
they do.

> Oh, and maybe let's also make more clear that `rx' always cares about
> implicit grouping when necessary.

No, there is no such thing in rx. The manual provides corresponding 
string-notation constructs for orientation only.
This is important -- rx forms are defined by their semantics, not by what 
strings they translate to.