Filtering for filenames beginning with lower case char

I have a lot of songs whith filenames that begin with a capital letter or a lower case letter or underscore or digit(s).

So to filter out filenames beginning with a lower case letter I tried

%_filename% MATCHES ^\l in the filter expression box.

But nothing happened. Then I tried

%_filename% HAS ^\l

But still nothing.

What is wrong with my filter expression? Could somebody please help?

From the help I found out that \l (lower case L) stands for any lower case character and and the caret mark searches in beginning of the filename and I coocked up the expression. But it did not work.

By default the matching is case insensitive. You can deactivate that:
%_filename% MATCHES (?-i)^\l

Thanks a lot! It worked wonderfully.
Is there an option to make it the default?
Thanks in advance!

There's no option for that.