XSLT: node()? vs node()*

Question

I've been working through some legacy code in XSLT in order to replace it with something in a more widely used language, and I've hit something about which I can't find a reference.

What's the difference between

<xsl:variable name="following_actions" as="node()*">

and

<xsl:variable name="following_actions" as="node()?">

I'm accustomed to seeing the asterisk version give me a list of records matching some condition specified in the body of the xsl:variable block, but I don't think I've seen the question-mark version before.

Directly relevant remedial references happily accepted. I believe I'm operating on XSLT 2.0, FWIW.

Answer 1

Like with regular expressions, ?, *, and + designate optionality and multiplicity:

• node() means 1 node.
• node()? means 0 or 1 nodes.
• node()+ means 1 or more nodes.
• node()* means 0 or more nodes.