John Lincoln from Ignite Visibility spotted a Google Hangout where Google’s John Mueller confirmed that Google will use URLs or domain names within content that are unlinked, i.e. without an a href attribute, to discover and index new pages of content.
John went on to add that typically no PageRank or trust is flown from an unlinked URL or citation, but Google may indeed use it for content discovery.
You can watch John Mueller from Google confirm this 47 minutes and 32 seconds into this video:
John Lincoln transcribed part of it:
We use those kinds of links to try to discover new content. So for instance if we see that someone has been writing about a new domain name and we can recognize that as a domain name in the text even without a normal HTML link there, then that is something where we will try to pick that domain name up, try to crawl it and index it and see if that is something worth including in our search results.
Sometimes it happens that we pick up a whole URL like that. Sometimes someone will try to shorter a URL with just a ‘…’ in between and we try to crawl that URL so we get it wrong. But our goal here isn’t necessarily to pass any pagerank, which we don’t do with those kinds of links. But rather discover new URLs that we haven’t seen before. And if we see someone write about a URL that we haven’t seen before we will pick that up and try to index that for search.
I believe this may be the first time Google has gone on record about how they use URLs or domains within content that are unlinked, i.e. basic citations.