in reply to Search and Replace Question
Privoxy does not actually use Perl. It uses Perl Compatible regular expressions, which means it supports mostly the same syntax for regular expression matching. Privoxy lets you apply regular expressions to the html page before it makes it to the browser.
For example, I use the following to filter out background images on some sites:
s|<body ([^>]*)background=\S+([^>])>|<body $1 $2>|ig
I am not completely sure what exactly you are trying to solve, but if you replace <body> with <body>"my stuff"</body> then all your html page will show is "my stuff". If you really do want to do that, I am not sure a forward lookup is needed. Untested code ahead:
s|<body>|<body>"my stuff"</body>|ig
|
|---|