DBD::mysql [...]

it does not document if "dbi" in lower-case will be accepted.

A DBD driver only prescribes the dsn-part after 'dbi:drivername:', and the DBI docs do document it; in fact, it actually does not document that uppercase DBI is accepted :-)

DBI connect

It says:

The $data_source value must begin with "dbi:driver_name:". The driver_name specifies the driver that will be used to make the connection. (Letter case is significant.)

So - the documented examples between the DBD and DBI modules conflict.

However, the code in DBI.pm resolves this conflict - it says:

sub connect {
 ....
 # extract dbi:driver prefix from $dsn into $1
    $dsn =~ s/^dbi:(\w*?)(?:\((.*?)\))?://i
            or '' =~ /()/; # ensure $1 etc are empty if match fails
[download]

so - it will accept EITHER case for the "DBI" part.

The part about "(Letter case is significant.)" applies to the DBD driver name, not the the "DBI" or "dbi" - it will even accept "DbI".

        What is the sound of Perl? Is it not the sound of a wall that people have stopped banging their heads against?
              -Larry Wall, 1992