Cookies can be set to various domain levels. Thus, cookies on www.this.domain.ext could be set to 'www.this.domain.ext', 'this.domain.ext' or 'domain.ext'. Cookies set to higher levels won't be visible on a different domain like 'www.that.domain.ext'! It will only see cookies set to 'domain.ext'. As merlyn said, they are sent everytime a request is made and all the ones you will ever see where you are, will be there. There is no way to get it so send the others.

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$you = new YOU;
honk() if $you->love(perl)