Saxon

Fixing the code that implements this rule to start searching at the function call itself, rather than at its parent instruction, fixes the problem for the normal case. However, when running with FeatureKeys.STRICT_STREAMABILITY set, the code is still reported as non-streamable, which appears incorrect.

STRICT_STREAMABILITY (a) suppresses some very early optimizations, like the elision of the node representing the xsl:sequence instruction from the tree, and (b) causes an early check on streamability before the main optimization pass. This early streamability check is passing. However, the xsl:sequence node is then elided during optimization, and we do another streamability check after optimization to build the actual execution plan, and this second check is failing because the "strict" flag is still set. It should probably only be set during the initial check.