It was noted in the NY F2F minutes:

In xsl:with-param, we might take into account the sweep of the expression
if the @as forces atomization.

In fact this is equally true for other variable binding elements.

I think we can add to the list of node-value contexts in section 19.3.1:

* The expression in the select attribute, or the contained sequence constructor, of an xsl:variable, xsl:param, or xsl:with-param element, if the element has an "as" attribute whose value is a SequenceType that exclusively permits atomic values and/or functions

* The contained sequence constructor of an xsl:variable, xsl:param, or xsl:with-param element, if the element has no "as" attribute

Rationale: both these situations prevent the value of the variable being a node in a streamed document.

In the list of node-value contexts we currently have:

* the select attribute of one of the instructions xsl:analyze-string, xsl:attribute, xsl:comment, xsl:copy, xsl:copy-of, xsl:namespace, xsl:processing-instruction, xsl:value-of

we should add xsl:message and xsl:assert to the list. We should also add the sequence constructors contained in all these instructions with the exception of analyze-string; in all these cases the supplied value will be either copied or atomized.