The "source" search

How do I use "source" in searching? It doesn't seem to work right for me. For example, searching favorites with "source:*pixiv*" returns far fewer images than expected. I can see more images in my favorites that are from pixiv and yet they don't appear when i search "source:*pixiv*".

The true source depends on the upload method. If they just plopped the page link into the source bar, it'll be https://www.pixiv.net/

If they expanded the image and plugged that into the source bar, it'll be https://i.pximg.net/

You can see which they used by going into the History of the post and what's under the source: in the tags.

To search for pixiv sources you can use pixiv:any. There's a plan to add a similar metasearch for other sites but it's not around the corner.