On which page this should be documented?

Jakub, adding it on the features.commandline pages might be ideal where the other command line switches for using php on command line is :)

The CLI and CGI information differs, so this report is now specific to 
fastcgi. There are several directives that appear specific to CGI:

  -b <address:port>|<port> Bind Path for external FASTCGI Server mode
  -C               Do not chdir to the script's directory
  -q               Quiet-mode.  Suppress HTTP Header output.
  -T <count>   Measure execution time of script repeated <count> 
times.

And several are specific to CLI, or at least are not showing up in the 
CGI help (sapi/cgi/php -h):

  -r <code>        Run PHP <code> without using script tags <?..?>
  -B <begin_code>  Run PHP <begin_code> before processing input lines
  -R <code>        Run PHP <code> for every input line
  -F <file>        Parse and execute <file> for every input line
  -E <end_code>    Run PHP <end_code> after processing all input lines
  -H               Hide any passed arguments from external tools.
  -z <file>        Load Zend extension <file>.
  args...          Arguments passed to script. Use -- args when first 
argument
                   starts with - or script is read from stdin

  --ini            Show configuration file names

  --rf <name>      Show information about function <name>.
  --rc <name>      Show information about class <name>.
  --re <name>      Show information about extension <name>.
  --ri <name>      Show configuration for extension <name>.

So, I suppose it's time to make features.commandline CLI and something 
else for CGI (which is now always FastCGI).

This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation better.