While using SGML/XML in applications described above some desires came up which would make things easier:
| | More means for DTD configuration in the SGML schema language. This means especially fully explicit occurrence operators. There should be an explicit operator for "required" (e.g. "!"). Furthermore there should be an operator for "not allowed here" (e.g. "^"). This would enable the DTD designer to use parameter entities to configure the DTD structure by manipulating occurrences.
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| | The content model of an element should be definable in respect of the actual context. There must be a meta DTD, defining the superset of all possible models, so that processors can rely on this. But in the actual context there must be limitations. These limitations cover mostly the occurrences. It could be done using architectural forms but then we must use different element names.
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| | Integrated documentation facilities. Actually a DTD is written and commented. But the comments are pretty weak and DTD syntax is not understandable by users who want to use the DTD in an authoring system. This documentation must cover the semantics, possible values etc. The content models must be described individually since the semantics of an element is content dependant.
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| | More means to express links using existing data. The locator attribute for example, could be the data of the locator element. Multiple nested link types can be established which reflect the mutual object hierarchy.
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