Subject: Characterstic Specification From: Vivek Agrawala <vivek@xxxxxxxxxxxxxxx> Date: Mon, 19 May 1997 14:30:13 -0400 |
Section 12.4.6 of the DSSSL standard has the following paragraph: > "An expression specifying the value of a characterstic shall be > evaluated with respect to two flow objects, which are referred > to as the _value flow object_ and the _specification flow object_. > The value of a characterstic for a flow object is determined by > evaluating the expression specifying that characterstic with > both the value flow object and the specification flow object > equal to that flow object." What does it mean to "evaluate an expression with respect to two flow objects" ? Is the evaluation of expressions in the DSSSL style language defined somewhere ? Also, are the terms "value flow object" and "specfication flow object" defined somewhere ? Further down in the same section, the standard says: > "[182] application-characterstic-declaration = (declare-characterstic > _identifier_ _string_ _expression_) > > .... The _string_ is a public identifier specifying the semantics > of the characterstic. If an implementation does not recognize the > specified public identifier, it shall ignore uses of the > characteristic. .... " The mechanism for specifying semantics of user-defined characterstics seems to be implementation defined. When the standard refers to an 'implementation' does it include only the style engine, or also the backends ? Jade's RTF backend currently supports some additional characteristics. I looked at the implementation, and it seems that the semantics are defined by the backend when it defines the FOTBuilder::Extensions. It is not clear to me how one defines that a certain charateristic is only available on a certain flow-object class. Currently, the public ids for these characteristics are of the form: "UNREGISTERED::James Clark//Characteristic::heading-level" Would it be possible to have more general public ids like, "UNREGISTERED::James Clark//Characteristic::integer" ? The name of the characteristic is already available as the first argument to declare-characteristic. -- Vivek Agrawala, Ph.D. Siemens Corporate Research, Inc. email: vivek@xxxxxxxxxxxxxxx DSSSList info and archive: http://www.mulberrytech.com/dsssl/dssslist
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