minor question of the difference between " and '

[WhatMeWorry via Digitalmars-d-learn]

string pwdxCommand = escapeShellCommand("pwdx", to!string(pid));
writeln("pwdxCommand = ", pwdxCommand);

Output:
    Current process ID: 7962
    pwdxCommand = 'pwdx' '7962'


I'm confused as to why the writeln statement didn't output "pwdx 
7962"?
Afterall, isn't that the definition of a string?  So what's up 
with the two groupings of single quotes?

BTW, those aren't backticks?  (think that is what the key is 
called)

Thanks in advance.