todo

* change all calls to reduce to not suppress division where appropriate
* store count in elements so we can have position of compile time errors
* failed parsing paths can add comments early

* fix indentation for @content, see @content tests

misc:

# sequence merging:

a b c d { color: red; }
x y z w  { @extend a; }

	a b c d, x y z w b c d { color: red; }


a b c d { color: red; }
x y z w  { @extend b; }

	a b c d, a x y z w c d, x y z a w c d { color: red; }


a b c d { color: red; }
x y z w  { @extend c; }

	a b c d, a b x y z w d, x y z a b w d { color: red; }

	x y z a b w d

	before: a b
	after:  d
	new: x y z w


a b c d { color: red; }
x y z w  { @extend d; }

	a b c d, a b c x y z w, x y z a b c w { color: red; }


->> new[:-1] . before . new[-1] . after
	
	new.len > 1
	before not empty