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Author: Christian Lieske

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Constraints in CSS

A look at vocabularies which can work with Cascading Stylesheets (e.g. XHTML and XML) reveals that they already have a means for capturing at least some of the constraints we have been discussing. To be specific, the CSS property "max-width" constrains box widths to a certain range.

Accordingly, with CSS we have the case were we may not want to enforce an ITS-specific representation of max-width but rather use what is already part of the native XML application (in the sense of the combination of XHTML instance and CSS). Of course, we need to make sure that the semantics and domain (in the sense of allowed values) of the ITS data category for constraints, and the are compatible.

Once we principally have come to the conclusion that the CSS "max-width" covers the ITS data category, we need to take care that the CSS representation makes sense to ITS aware applications. This may require:

1. a mapping declaration (see our discussion at http://esw.w3.org/topic/its0504ReqPurposeSpecMap) 2. possibly special locator processing

With 'locator processing' I refer to the situation in which a linking mechanism is used in order to associate a vocabulary with a stylesheet. Examples:

A) Via special element: <LINK REL=StyleSheet HREF="style.css"

TYPE="text/css">

B. Via processing instruction: <?xml-stylesheet type="text/css"

href="style.css" media="all"?>

Obviously, in these case, processing expectations related to the mapping declaration are different from the ones where "internal" styling (ie. either with the "style" element or the "style" attribute) is used: Actual values are not related in the XML instance but rather externally.