Base URL
The upstream library provides very basic base URL functionality via a static variable, this library follows RFC 3986 a little closer.
Here are a few examples to demonstrate how it works:
$browser->setBaseUrl("http://example.com");
$browser->visit("/stuff"); # http://example.com/stuff
$browser->setBaseUrl("http://example.com/account");
$browser->visit("section"); # http://example.com/account/section
$browser->visit("/section"); # http://example.com/section