p:assert

[JDziurlaj]

p:assert functions as an assert in other languages, such as xsl. It takes in a XPathExpression coerced to a boolean if required, and throws a dynamic error if the assertion fails.

<p:assert
  name? = NCName
  test = XPathExpression
  code = QName
</p:assert>

I am not sure if collection? is required here, I don't use it. It may be useful for this step to have a port that can be used to construct the error, akin to p:error.

[xatapult]

I suppose you are suggesting adding a p:assert to the step library? That sounds like something for the https://github.com/xproc/Vnext repository... Shall I transfer it to there?

[ndw]

I happened to want exactly this step just the other day. You can do approximately the same thing with:

<p:if test="..."><p:error code="..."/></p:if>

but that's not as neat.