Can someone explain nginx conditional flags? (-f, -d, -e, etc)

I'm in the process of migrating from Apache to nginx and have used http://winginx.com/en/htaccess to migrate the rewrite rules. I'm trying to understand what the translated ones mean though and I can't find any documentation on it. Here's an example:

if (-e $request_filename){
    rewrite ^(.*)$ /index.php break;
}

I believe -f checks if a file exists, and -d checks if a directory exists, but what about -e? And where might I find these in the documentation? Thank you!

According docs:

• checking of a file existence with the -f and !-f operators;
• checking of a directory existence with the -d and !-d operators;
• checking of a file, directory, or symbolic link existence with the -e and !-e operators;
• checking for an executable file with the -x and !-x operators.