[Greasemonkey] Can anybody explain to me the strange namespace rule?

[Linan Wang]

I noticed that in greasemonkey scripts, to add a link in a page call a self
defined function, have to 'hook' the function into the unsafeWindow. For
example:

var alink=document.createElement('a');
a.innerHTML='A link';
a.href='javascript:self_defined_function()';

unsafeWindow.self_defined_function=function(){
     another_function();
};

function another_function(){}

It is understandable, but in the 'self_defined_function', if i want to call
another function defined in userscript, that function should NOT be hooked
into unsafe. Why? Can anybody explain to me?

Many thanks!

Best regards

Linan Wang