Today's question comes from Computer Klaus in Sao Paulo, Brazil.
Computer Klaus wants to know, "Hi! How does Google see cross-domain canonicals?"
Great question.
Whenever rel="canonical" was first introduced, we wanted to be a little careful.
We didn't want to open it up for potential abuse.
So you could only use rel="canonical" within one domain.
The only exception to that was, you could do between IP addresses and domains.
But over time, we didn't see people abusing it a lot.
And if you think about it, if some evil, malicious hacker has hacked your website, and he's going to do something to you, he's probably going to put some malware on the page, or do a 301 redirect.
He's probably not patient enough to add a rel="canonical", and then wait for it to be recrawled and reindexed, and all that sort of stuff. So we sort of saw that there didn't seem to be a lot of abuse.
Most webmasters used rel="canonical" in very smart ways.
We didn't see a lot of people accidentally shooting themselves in the foot, which is something we do have to worry about.
And so a little while after rel="canonical" was introduced, we added the ability to do cross-domain rel="canonical"s.
And it basically works essentially like a 301 redirect.
If you can do a 301 redirect, that's still preferred because every search engine knows how to handle those, new search engines will know how to process 301 permanent redirects.
But we do take a rel="canonical", and if it's on one domain and it points to another domain, we will typically honor that.
We always reserve the right to sort of hold back if we think that the webmaster is doing something wrong or making a mistake.
But in general, we will usually, almost always abide by that.
Hope that helps.