[xsl] How is fold-left useful to XSLT streaming?

["Costello, Roger L." <costello@xxxxxxxxx>]

On Friday, November 22, 2013 Michael Kay wrote:

> There are plenty of techniques still available for
> streamed processing: accumulators, xsl:iterator,
> fold-left, xsl:fork.

I understand the usefulness of accumulators, xsl:iterator, and xsl:fork to
streaming.

I am unclear on the usefulness of fold-left to streaming.

Would you (Michael or anyone) provide an example to illustrate the usefulness
of fold-left to streaming please?

/Roger