Re: [xep-support] Marker values in expressions

From: G. Ken Holman (
Date: Thu Jan 22 2004 - 04:58:30 PST

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    At 2004-01-22 17:51 +1100, Ben Reid wrote:
    >Would I be right in saying that you cannot use <fo:markers> and
    >in calculations?

    Correct, though you can use markers to store the results of calculations
    made at transformation time to be retrieved at rendering time.

    >That is if I define a value using a marker, it cannot be accessed through
    >an expression
    >in an <xsl:value-of select=""/>.

    Correct, it cannot. <xsl:value-of/> is an expression in XSLT and the
    *result* of XSLT is passed on to an XSL-FO engine for rendering without any
    feedback loop.

    My first comment is that you can repetitively calculate intermediate totals
    from a stream of data, seeding the result in a marker at each stage with
    the intermediate total at that stage, and then when the FO engine lays out
    a page it can retrieve into static content the first or the last of the
    markers from the page to allow you to render that particular intermediate
    result (of the very many that you calculate) on the page in which the
    result appears.

    Note that XSL-FO *does* have an expression language, but only for property
    values and not for displayed values. If you have a complex property value
    calculation you can simplify your work by producing an expression in the
    property that gets calculated by the FO engine, rather than making
    contortions in your XSLT to figure that value out.

    I hope this helps.

    ................ Ken

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