Whitespace-only text nodes are removed from the source tree for elements
named by strip-space before transformation, with preserve-space and a
more specific name test winning over *, and xml:space=preserve on a
source element or ancestor overriding the stripping. The name sets fold
across xsl:include/xsl:import. Refactors the stylesheet compile loop
through a Parts accumulator to absorb the new top-level elements within
the complexity budget.