The use of named formatting properties to influence the presentation of documents on the web has grown from its introduction in to include a wide range of specifications: , , , , , and possibly others.

This has a positive benefit for the user- and developer-communities because it reduces the number of property languages that need to be understood by users and applications. Furthermore, as XML vocabularies are now being combined in many ways, it is becoming more than merely beneficial, it is becoming imperative that a common set of properties and values be developed.

Consider an application that is expected to render a compound document that consists of XSL Formatting Objects, XHTML table markup, SVG diagrams, and MathML equations. Typically, the author (and the reader) would want consistent styling for all these pieces.

Because many properties are considered inheritable, each of the vocabularies must use the same properties for the same purpose in order for the styling to be consistent. In addition to using the same properties, the interpretation of those properties must be the same in each vocabulary.

Consider a simple concrete example, where only two vocabularies are nested:

In the absence of any other direction (from an external stylesheet, for example), one imagines that selection of a font family and size on the XHTML div element applies to both the the XHTML text and the SVG text.

It would be architecturally unsound to suggest that different vocabularies should specify the same or very similar traits using different property names or values. In this particular case, for example, it would be unsound to suggest that the font-family property be used to influence XHTML text but the fontFamily property be used to exert the same influence over SVG.

The CSS, HTML, SVG, and XSL Working Groups have a shared history of successful coordination on formatting properties and values. It is possible that specific actions could be taken to assure continued coordation: establishing key liasons, formation of a coordination group, or even broad reorganization of the specifications.

However, these actions are outside the scope of this finding which aims simply to specify an architectural principle.

Formatting property names, values, and semantics must be consistent across all specifications. Whenever a working group suggests the creation of a new formatting property, or the addition of, or a change to, an existing formatting property's allowed values, the working group must show a strong justification for not using an existing formatting property or properties that are related to the proposed new property or value.

Clearly innovation on the web will create situations where new properties are required and existing properties will need to be extended. What we must avoid doing is changing the semantics of existing properties in ways that introduce unnecessary interoperability issues.