Depends on how Mason (which I have no idea about) handles embedding its own stuff in the markup. If it uses processing instructions (<?foo · · · ?>) then HTMLTidy may reindent the opening part of the tag (<?foo) at will and may reindent any following lines as a block, but it won't touch the content. For the majority of languages that means there should be no change, though it might not be what you want.

Unfortunately - and that is the one thing that annoys me about HTMLTidy -, there's no way to specify a list of candidate tags for reindenting or a list of tags not to reindent.

Mason is having several forms to markup its own stuff. And it's pretty unique. E.g.

% my $str = "This line is Perl until the linefeed."; # cannot contain 
+whitespace at the beginning!!!

<%perl>
my $str2 = "This is a Perl block";
</%perl>

<%args>
$a   # this is a special block 
$b
</%args>

<h1>Hello <% $monkname %>!</h1>

It is <& /lib/mason_components/weather_forecast.mas, fmt => 'Celsius' 
+&> celsius degrees outside!
[download]

etc. I guess I will try to run Tidy, but not confident about it at all :-/

--
tune