---------                  -----------------
          |         |   form data    |                  |
          |         | -------------> |    -----------------
          |         | -----------------> |                 |
   -----> |         |   HTML content |   |                 |
  browser |  Apache | <------------- |   |                 |     
   <----- |         | <----------------- |   child         |
          |         |   error msgs   |   |   process       |
          |         | <------------- |   |                 |
          |         | <----------------- |                 |
           ---------                  ---|                 |
                                          -----------------