It is impossible to suppress initial HTML preamble for directories, i.e.
<HEAD><TITLE>Index of dir</TITLE></HEAD><BODY>
It means that it is impossible to change <TITLE> or add any
<META HTTP-EQUIV...> tags to <HEAD> section or change <BODY>
attributes without HTML syntax violation (.asis, cern_meta, etc.
not helps here too).
Fix:
I add "SuppressHTMLPreamble" option to "IndexOptions". When this option
is set _and_ HEADER.html (or what you set as it) is present and readable,
standard <HEAD><TITLE>Index of dir</TITLE></HEAD><BODY> preamble
will be suppressed assuming you have right HTML preamble in your
HEADER.html. It solves all problems mentioned above.