Lighttpd

I've gone through the docs several times, I'm either missing something, or it's not discussed in the docs. I'm happy to RTFM, if I know where in the TFM. But for someone relatively new to the docs, please consider that what I noticed isn't intuitive.

Looking at the default config file, we see:

fastcgi.server             = ( ".php" =>
                               ( "localhost" =>
                                 (
                                   "socket" => "/var/run/lighttpd/php-fastcgi.socket",
                                   "bin-path" => "/usr/local/bin/php-cgi" 
                                 )
                               )
                            )

But when looking at the syntax in fastcgi module documentation (and others: proxy.server, etc), it doesn't mention "localhost" at all, rather just the double "(".

Docs:Configuration
Docs:ModFastCGI

From other spots around the net, I see that the "localhost" parameter can be replaced by 0 or some non-zero number of actual hostnames. But I don't think this is mentioned anywhere in the docs. All the docs show is:

fastcgi.server             = ( ".php" =>
                               ( (                                 (
                                   "socket" => "/var/run/lighttpd/php-fastcgi.socket",
                                   "bin-path" => "/usr/local/bin/php-cgi" 
                                 )
                               )
                            )

From the doc page, how are we supposed to know that hostnames could be there, or that the parameter is even optional? Are there other types of strings besides hostnames that can be here?

Thanks!