Microsoft有一个提供the CLSID and ProgIDs of various MSXML 4.0个对象的页面：
Symbolic Name: CLSID_DOMDocument40
GUID: {88d969c0-f192-11d4-a65f-0040963251e5}
ProgID: Msxml2.DOMDocument.4.0
Symbolic Name: CLSID_XMLSchemaCache40
GUID: {88d969c2-f192-11d4-a65f-0040963251e5}
ProgID: Msxml2.XMLSchemaCache.4.0
但是我的Vista机器或同事的XP机器上都没有注册ProgID或CLSID.
> MSXML 4.0是否仅随某些版本的Office(例如Office 2003)一起提供？
>它最初是否附带Windows XP,但后来的服务包将其删除了？
>是否存在安全漏洞,并且已被删除？
>它被简单地描述了吗？
我愿意转向MSXML 5.0,它可以在Windows XP和Windows Vista机器上使用 – 但我想确保我拥有最广泛的兼容性;我认为MSXML 4.0比MSXML 5.0更广泛.
微软做recommend that i use MSXML 6.0：
It is recommended that you upgrade
from earlier versions of MSXML to
MSXML 6.0. MSXML 6.0 provides security
and performance improvements over
earlier MSXML versions.
在该博客条目的“MSXML生命周期和历史”部分中,作者声明：
MSXML4 was a predecessor to MSXML6
but hasn’t ever shipped in the
operating system. MSXML6 is a
significant step forward in terms of
reliability,security,W3C and
System.Xml compatibility,and it also
has support for native 64-bit
environments. Right now we are
investing much more heavily in MSXML6
and MSXML3 and we’re encouraging our
customers to move to 6 when possible
and 3 when necessary.
OP编辑：重要的是要注意MSXML3是在W3C决定最终的XSD规范之前发布的.最终,W3C使用的XSD语法与Microsoft为MSXML3创建的语法不同. MSXML6与W3C选择的XSD方案完全兼容.
这意味着MSXML3和MSXML6彼此不兼容;和MSXML3不使用标准XSD.
