The refexpr expression allows access to stored reference values and is represented in the xfMap by the <refexpr> element.
The general syntax for the element is:
<refexpr expr=”...” default=”...” reference-group=”...” r-stack=”...”> <arg> ... optional reference name as expr seq ... </arg> <arg> ... optional default value as expr seq ... </arg> </refexpr>
The expr attribute denotes the name for a stored reference. The optional default attribute may contain the value returned by the expression in the case that a reference by that name is not found in any of the constructed reference-sets. This may occur if the reference was never stored or if the reference-set containing that reference was already destroyed.
Both <arg> child elements in the <refexpr> element are optional.
The expr attribute is required but it may be the empty string, in which case the first <arg> child element must be present, and the evaluated expression sequence for this first argument becomes the reference’s name to search.
If the default attribute is absent or if it is present but its value is the empty string, then the second argument, if present, is evaluated to become the default value for the expression in the case that the reference is not found.
The reference-group attribute is optional and it specifies the group-name for a reference in a reference-set. If the reference-group attribute is absent, then the default group in a reference-set is assumed.
The r-stack attribute is optional and it specifies the starting place to search for values in the stack of reference-sets. The valid values for the r-stack attribute are top, previous and bottom, with top being the default value.