Extend of extend all

Extend all will extend selectors generated by normal extend, however normal extend ignores selectors generated by extend all. Was that intentional?

I do not care one way or the other, I just need to know whether it is a bug or a feature.

Normal extend ignores selectors generated by extend all:

ruleset:last {
  property: value;
}

full:extend(ruleset:first) {}
:first:extend(:last all) {}

compiles into:

ruleset:last,
ruleset:first {
  property: value;
}

Extend all will extend selectors generated by normal extend:

ruleset:last {
  property: value;
}

full:first:extend(ruleset:last) {}
:nth-child(3n):extend(:first all) {}

compiles into:

ruleset:last,
full:first,
full:nth-child(3n) {
  property: value;
}

If it is a bug, then it is related to #1641 .

Start by reproducing the two selector examples from issue #1667 and compare how normal extend and extend all process generated selectors. Read the related issue #1641, then determine whether the asymmetric behavior is intentional or needs a consistent change; done means the behavior is decided and documented or corrected with matching results.