1. Subqueries
AFIK the expression {{#ask: [[propname::<q>a subquery</q>]]}} today means
a page's property must equal ANY value in subquery results to be selected
into a result set.  Isnt {{#ask: [[propname::[[v1]][[v2]]]]}} the same thing that's
being produced by the parser? However from the user manual about the
OR operator, both these queries yield an equal result set:
{{#ask: [[propname::v1]] OR [propname::v2]]}} ... and ...
{{#ask: [[propname::v1 OR v2]]}}
Suggesting subqueries need a 'sep' arg (default=OR) for specifying whether
the result set is to be a disjunctive, conjunctive, &or negated, expression.
2. Result Formats
It would be nice to specify that a result set is composed of data values for a
property, so that a template specification would, for instance, be applied
against each of the values of the template, or a table specification would
create a row of cols.