Hello!

I have a couple of general questions about expl3.

- Are all boxes and coffins made so that their content is wrapped in a TeX group?
More specifically, is it safe for code to assume that all box/coffin content is
implicity grouped?

- Many functions in expl3 are of the form a := func(b, c) (e.g. \str_concat:NNN,
\seq_set_map:NNn) or a := func(b) (e.g. \int_set:Nn, \tl_set:Nn).
Sometimes, one will want to write code like a := func(a, b) or a := func(a),
that is, directly assign a new value to a variable based on its current value.
Is it ever safe to write such code in expl3?

Warmly,
Kelly