Global code is that source text that is outside of all function declarations.
On initialization of some global code into an execution context, the scope chain is initialized to only contain the global object and nothing else.
Variable instantiation is performed using the global object as the variable object and with empty property attributes.
The this value is set to point at the global object.
ECMA 262 edition 2 - section - 10.1.2
ECMA 262 edition 2 - section - 10.2.1
ECMA 262 edition 3 - section - 10.1.2
ECMA 262 edition 3 - section - 10.2.1