The attached patch enables assignment of and reference to parameters
prefixed with ksh-style namespace syntax, e.g., ${.namespace.param}.
As yet, there's no special significance to use of this syntax, that
is, parameters having such a prefix are ordinary parameters like any
others, with the usual dynamic scoping rules, etc.  Each of namespace
and param must be an identifier in the original zsh semantics of
identifiers.

The braces are required when using this syntax in a parameter
substitution, so without braces $foo.bar continues to be interpreted
as ${foo}.bar.