[users@httpd] Where does ap_rprintf actually print out?

[eeadev dev]

Writing an apache C module I tried this function:

https://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d

but I dont know where it does print out. Does it in any specific file?

I called it this way:

 ap_rprintf(r, "print out!");
and checked in the error.log nor in the access.log