HL — container element for history elements
A HL is simply
a container element for one or more HN elements.
A BATCHLOG always records at least the date and time of
the current batch execution, and if history is enabled, additionally
records the date and time of every previous execution.
The HN child elements can be ordered in reverse
chronological order by descending sequence of
fd.
While the oldest HN element generally has a
value of 1 for this attribute, this
is not required.
Similarly, it is not required that there are no gaps in the ascending
sequence of fd attributes, but this
is usually the case.