Thanks, defining an input_filter did the trick °

$twig=XML::Twig->new(
    #discard_spaces => 1,
    input_filter => sub { $_[0] =~ s/^\n//r },
);
[download]

Also found discard_spaces but couldn't make it work though.

updated

or rather not !

I checked all calls to the callback, and the input filter is run on each line of input.

I.e. it will also discard newlines in the middle of a content.