It would be helpful to have a definitive list of available elements.
One XT3TS test (try-013) expects "catch" to be available, but it isn't marked in the specification as "Category: instruction" (e.g. in C Element Syntax Summary (Non-Normative).
The test states:
<!-- Element-available on xsl:try and xsl:catch - true in 2.1, false in 2.0 -->
Elements xsl:merge-key, xsl:merge-source and xsl:on-completion are similarly not categorized.
The WG decided it would make sense to change the rules for element-available() so that it returns true for all XSLT elements and not only for those that are classified as instructions.
Changes applied (draft N)