vibe.d Subdirectory?

[seany via Digitalmars-d-learn]

I am new to vibe.d and plying a bit with it.

I notice, that in case of Apache, there is a "root" directory, 
often by default under /var/www or /srv/http (resp. ftp) if you 
are using linux, and then every time the client sends a request, 
apache looks in to the root directory, deduces the subdirectory 
from the URI, and pulls the page up from there. Then it parses 
the PHP / other scripting commands, and prints the HTML as is, 
before serving it over http.

I want to know the equivalent of all these in vibe.d. The website 
has a documentation, but all what I find is that you will need an 
app.d, in a predefined directory structure. I however, do not 
understand, what the root directory is going to be.

Is it going to be the directry where vibe.d is started?

Say, I start my vibe.d under /server, then I have an app.d under 
/server/a/app.d and /server/b/app.d

Do I access them via http://top.level.domain/a, resp /b, and 
app.d is like index.html / index.php which vibe.d looks for by 
default, or do i have to use http://top.level.domain/a/app.d