code: @Beta
      public PutItemSpec withExpressionSpec(PutItemExpressionSpec xspec) {
          return withConditionExpression(xspec.getConditionExpression())
                .withNameMap(xspec.getNameMap())
                .withValueMap(xspec.getValueMap())
                ;
      }
docs: Convenient method to specify expressions (and the associated name map and
  value map) via {@link PutItemExpressionSpec}.