Why I'm calling this a pre-release.

The systems works surprisingly well in most cases, but there is a clear need to get better error handling for debugging. What is needed is:

• Checking of content elements and appropiate error messages for content elements that are not allowed. (Currently any inappropriate content element is just ignored)
• Checking of appropriate attributes for each element (and the proper error message when not allowed)
• Checking of appropriate attribute values for each attribute. (and the proper error message when not allowed)