documentation of second param %attr of $dbh->prepare() and $dbh->do() missing

[peterdd]

What is the purpose of that %attr param? Examples in the DBI documentation always use undef and I found no explanation of what %attr should/can be.

One might think it is the same as described by $dbh->clone() if someone reads the documentation in chronologic order, but who does that and it is ambiguous.