Saxon

The stylesheet should report errors (assuming you're not running with target:JS), because it calls constructs that aren't available in Saxon/J, such as ixsl:schedule-action and xsl:query-params(). But of course it shouldn't fail with an NPE.

I think the reason it's crashing is that it's a bit inconsistent as to whether the children of ixsl:schedule-action are treated as instructions or not.

The relevant rule for the xsl:schedule-action element is:

[ERR XTDE1450] When a processor performs fallback for an extension instruction that is not recognized, if the instruction element has one or more xsl:fallback children, then the content of each of the xsl:fallback children must be evaluated; it is a dynamic error if it has no xsl:fallback children.

But in fact we won't get that far: the instruction will never be evaluated because the stylesheet contains errors (the call on ``xsl:query-params()`).

If we had no knowledge at all of the xsl:schedule-action instruction, then I think it's an open question whether we should validate the contained xsl:call-template: I don't think the spec answers this question. But the crash occurs because we are doing half the work of validating it, and not the other half. Given that we do have knowledge of the instruction, I think it makes sense to validate the contained instruction fully.

The solution is for TextValueTemplateNode.parse() to catch any error thrown by the call on AttributeValueTemplate.make(), and report it via StyleElement.compileError(), rather than letting it bubble upwards causing the processing of the containing component to be abandoned.