Preliminary:
When using this property to sequence through elements,
the sourceIndex of the selected element may be lower than that of the element selected,
thus halting sequential progress in a frenglish auto loop ...
eg. (reduction from a large document with maybe-1000 of these)
<DL><DIV>
<DT>...<DD>...<DT>...</DT><DL><DT>...</DT></DL><DT><B>frenglish</B><DT>...</DT>
</DIV></DL>
Selecting 'frenglish' from tags('B') will drop to select its enclosing <DT></DT>, and loop-halt.
[I've also seen this occur in descending-order, but haven't traced it yet. Ray.]
[Equally apparent is that Ctrl-B fails to return such a spot to non-bold.]