Any HTML markup generated by a web content management system should be customizable. This includes everything from the opening html tag to forms. If the system creates tags they should be customizable by the site publisher.
Why? This provides maximum flexibility to the site owner in deploying their desired template and overall design. Sounds like a no-brainer, huh?
You might be surprised how often this can be an issue, particularly with content management systems that are not very mature or have not been updated in a while. It creates many headaches in deploying web site designs and might even prevent the site owner from deploying the best possible design for their needs.
Add this to your list of key things to assess when reviewing web content management system.
C. David Gammel, CAE 
I was just thinking about this today.
I call this “infiltrating the client,” and it drives me nuts. Why? Because Ektron does it all the time. All their controls output HTML, and in many cases, you can’t change it.
I’ll go a step further, and say this:
“If your CMS emits HTML, you are required to have enough API hooks to ensure your developer can get at that same functionality using his own HTML. If the only way to some functionality is through some of your pre-rolled HTML, then you did it wrong.”
Right on, Deane. Even a simple library of templates that can be easily accessed to alter system-generated markup would suffice.
I may have to eat crow here. I was just looking through an Ektron install I have, and I found a bunch of XSLT files that look like they control the output of the server controls.
If that’s true, then Ektron has my apologies. But the basic point I got up on my high horse about is still valid…