I'm going to amend my suggestions after thinking about it again:

 > The arguments are either a single expression or a subexpression in
parentheses. When it is a subexpression in parentheses, the arguments of
the call are separated by spaces.

This should read

 > The arguments are either a single expression or a list subexpression.
When it is a list subexpression, the arguments of the call are parsed
from the elements of the list.

Your text:

 > When argument of a call, spaces are interpreted as separating arguments.

Should be:

 > The arguments of the call are parsed from the elements of the list.

___________________________________________

These changes reflect the fact that i.e. f(- x) is a single argument,
not two arguments.

(They don't address the ambiguity issue Marc pointed out. Because
"unquote" is probably not valid in the expression, adding "unquote" as
the argument separator probably works, even if it seems hacky. The above
might change in such a scenario.)

-- Peter McGoron