code: @Beta
      public QuerySpec withExpressionSpec(QueryExpressionSpec xspec) {
          return withKeyConditionExpression(xspec.getKeyConditionExpression())
                .withFilterExpression(xspec.getFilterExpression())
                .withProjectionExpression(xspec.getProjectionExpression())
                .withNameMap(xspec.getNameMap())
                .withValueMap(xspec.getValueMap())
                ;
      }
docs: Convenient method to specify expressions (and the associated name map and
  value map) via {@link QueryExpressionSpec}.