asp.net mvc - What does 'the URL is local' mean? -

i debugging code , there check (in asp.net mvc controller)

if (url.islocalurl(returnurl)) 

so check documentation , says returns value indicates whether url local.

but mean, 'the url local'?

if hit webserver, when webserver 'the url local' ?

in asp.net mvc blog preventing open redirection attacks (c#) can find explanation of why should use it, but, tradition mvc's documentation, it's not explained how works.

you can read source presented there though: checks whether url starts / or ~/, meaning: whether relative url thereby points same domain.