def expr_query(criterion)
      selection(criterion) do |selector, field, value|
        if (field.is_a? Key) && custom_serialization?(field.name, field.operator)
          specified = custom_specify(field.name, field.operator, value)
        else
          specified = field.specify(value.__expand_complex__, negating?)
        end
        selector.merge!(specified)
      end
    end
def expr_query(criterion)
      selection(criterion) do |selector, field, value|
        if (field.is_a? Key) && custom_serialization?(field.name, field.operator)
          specified = custom_specify(field.name, field.operator, value)
        else
          specified = field.specify(value.__expand_complex__, negating?)
        end
        selector.merge!(specified)
      end
    end
Create the standard expression query.

 @api private

 @example Create the selection.
   selectable.expr_query(age: 50)

 @param [ Hash ] criterion The field/value pairs.

 @return [ Selectable ] The cloned selectable.

 @since 1.0.0