#761 Specification for @match in att.scoping is confusing

[Martin Holmes]

The definition of @match in att.scoping says this:

supplies an arbitrary XPath expression using the syntax defined in Kay (ed.) (2007) which identifies a set of nodes, selected within the context identified by the target attribute if this is supplied, or within the context of the element bearing this attribute if it is not.

whereas the remark at the bottom says this:

The expression of certainty applies to the nodeset identified by the value of the target attribute, possibly modified additionally by the value of the match attribute. If neither attribute is present, the expression of certainty applies to the context of the certainty element itself, i.e. its parent element.

The one seems to mean that <certainty> (for instance) is the default XPath context, while the other means that <certainty>'s parent is the default context. But in fact it's more subtly confusing than that; the one refers to the @match attribute, while the other refers to the expression of uncertainty itself. This is such a potential source of error that I think it needs to be reviewed, and it should also be illustrated with more examples. Finally, I think we should strongly suggest that @target be used, to avoid this concern.