For example, edit this template:
Admin CP -> Styles & Templates -> Style Manager -> « » -> New Posting Templates -> newreply
Add the red code near the top:
Code:
$stylevar[htmldoctype]
<html dir="$stylevar[textdirection]" lang="$stylevar[languagecode]">
<head>
$headincl ude
<title>$vboptions[bbtitle] - $vbphrase[reply_to_topic]</title>
</head>
<body$ onload>
$...



