Stackable.info is a web based content editor utility, that is devoted to the importance of well structured content. Most editor utilities are focused on "appearance" to the detriment of sensibly structure (i.e. whatever it takes to make it look good). Stackable.info ensures that edited content stays in the well formed realm.
Objectives are to allow an admin to enforce markup structure on content, and give editors the freedom and ease to create any content that is within that prescribed structure.
Stackable.info is not a WYSIWYG editor, because although a WYSIWYG editor may make content look good, the structure of the content is hidden from the editor, and the markup often takes a circuitous route into overly nested tags in order to achieve the appearance of well structured content.
The Tact that Stackable.info takes is to be upfront with the editor by showing them their content's structure, and enable them to easily create "in-bounds" content. Stackable.info champions a separation of "style," from "structure" to make the process of "content editing," a rational activity. A little demo here.
A Graph of Tag Structure
The structure of the tags that you deem to be "in-bounds" are specified with a graph of tags and the parent/child relations between them. Each node of a "tag-structure graph" represents an HTML tag, and each edge delineates the acceptable relations between them.