The HTTP request phases themselves have not changed from mod_perl 1.0, except the PerlHandler directive has been renamed PerlResponseHandler to better match the corresponding Apache phase name (response).
The only difference is that now it's possible to register HTTP request input and output filters, so PerlResponseHandler will filter its input and output through them. Figure 25-3 depicts the HTTP request cycle, which should be familiar to mod_perl 1.0 users, with the new addition of the request filters. From the diagram you can also see that the request filters are stacked on top of the connection filters. The request input filters filter only a request body, and the request output filters filter only a response body. Request and response headers can be accessed and modified using the $r->headers_in, $r->headers_out, and other methods.