模式更改不起作用

我有一个名为a.rnc的架构，看起来像这样

default namespace = "urn:schemas-foo:bar"
include "b.rnc" {
        start = A
        Links = element link { HidableLinkType }*
    }

A = element Bat { AType }

AType = SavedResourceType 
                & Boundary?
                & Baz*
                & element link { HidableLinkType }*

我还有一个称为b.rnc的架构，该架构以前看起来像这样

default namespace = "urn:schemas-foo:bar"
include "c.rnc"
include "d.rnc" {
        start = Baz
    }

Baz = element Z { BType }

BType = SavedResourceType

SavedResourceType &= Boundary?
                  &  element panel-id { text }?
                  &  Annotations?                          

Boundary = element boundary { "a" | "b" | Bounds }

Bounds = (
        attribute from { xsd:date },
        attribute to { xsd:date }
    )

但是我将最后一位（因为xml结构已更改）更改为

Boundary = element boundary { Bounds }

    Bounds = (
            attribute from { "a" | "b" | xsd:date },
            attribute to { "a" | "b" | xsd:date }
        )

我已经生成了rng文件，但是当运行一些针对这些模式进行验证的代码时，出现以下错误

POST <url> 400 (Invalid attribute value is found. Value = 'a' Expected elements are: . line 7, column 13   Validated using schema:   b.rng) 

我在这里做傻事吗？