In MSHTML, what do the numbers mean? Like in IHTMLElement7?

Question

In MSHTML the interfaces are often numbered. The numbers are at the end of the interface names like IHTML{name}{number}. Interfaces like:

• IHTMLRuleStyle
• IHTMLRuleStyle2
• ...
• IHTMLRuleStyle6

or

• IHTMLElement
• IHTMLElement2
• ...
• IHTMLElement7

A list can be seen in this Microsoft page

Answer 1

Thanks @Jay for your comments.

The numbers represent the version of MSHTML and the version numbers have an indirect relationship with the version of Internet Explorer, CSS, HTML, etc...

I wish I had did this search before but Geoff Chappell's site has a great chart mapping versions of MSHTML to IE and Windows.

Versions of things
MSHTML  IE      Windows
6.0     6.0     Windows XP
6.0     6.0     Windows Server 2003
7.0     7.0     Windows Vista
8.0     8.0     Windows 7

Judging from the chart, the version of MSHTML is closely related to the version of Internet Explorer.