---------                  -----------------
          |         |   form data    |                  |
          |         | -------------> | stdin            |
          |         |                |                  |
   -----> |         |   HTML content |           CGI    |
  browser |  Apache | <------------- | stdout    script |
   <----- |         |                |                  |
          |         |   error msgs   |                  |
          |         | <------------- | stderr           |
          |         |                |                  |
           ---------                  -----------------