XSLT streaming: the processor "remembers" things as it

Hi Folks,

Consider an XSLT program that is at some node. The XSLT streaming rules say
that the following nodes are accessible from that node: its ancestors and
their attributes and namespaces, and its descendants and their attributes and
namespaces.

If my XSLT program accesses ancestor nodes, that seems to require the XSLT
processor to back up. And isn't that a violation of the fundamental law of
streaming, "The XSLT processor shall not back up"?

Or, perhaps my XSLT program can access ancestor nodes because, as the XSLT
processor descends the XML tree it keeps a record of each node through which
it descends (the node's name, its attributes, its namespaces). Yes, that must
be what the XSLT processor does. Suppose that my XML tree is very deep, then
the XSLT processor will have to remember a lot of stuff, right? In the extreme
case, every node in the XML document has no siblings, just one child. Thus,
the XSLT processor would have to remember the entire XML document, right?

Questions:

1. In XSLT streaming the processor "remembers" things as it descends the XML
tree, right?

2. In XSLT streaming, allowing access to ancestors seems like a bad idea, for
the reasons described above. What is the rationale for allowing access to
ancestors?

/Roger