The primary link of this entry. Most feeds use this as the permanent link to
the entry in the site’s archives.
If this is a relative URI, it is
resolved according to a set of rules.
Some RSS feeds use guid when they mean link. guid
can also be used as an opaque identifier that has nothing to do with links. If
an RSS feed uses guid as the entry link and no link
is present, Universal Feed Parser detects this and makes the guid
available in entries[i].link.
In other words, you can always use entries[i].link to get the entry
link, regardless of how the feed is actually structured.