Who is "it" in "its"

[wuzhouhui]

Hi,

I'm reading the appendix A of svnbook, one sentence says:

> While Subversion is able to use Apache HTTP Server (or, httpd) as one of
> its network server programs, its dependence on APR does not mean that
			       ^^^
> httpd is a required component.

I'm just a little confused about "it" in "its", who is "it"? httpd or
Subversion?