Ultimately, I think we'll have the following constructors:

my $parser1 = HTML::TokePaser::Simple->new($file); works
my $parser2 = HTML::TokePaser::Simple->new($file_handle);
my $parser3 = HTML::TokePaser::Simple->new_from_scalar($string);
[download]

why not additionally:
my $parser5 = HTML::TokePaser::Simple->new($string);
i think XML::Simple does that. it looks at $string and decides of it's xml or a filename. maybe that's possible for your module, too?
update: just saw that something like that was already suggested.