frankly, I don't understand what you mean with "(...) what these databases are (...)". Do you relate to a specific function of Safari (e.g. in Preferences > Advanced > Database storage)?
Hi Lyndsay. If you mean in the preferences for Safari:
Yes, I hate that you can no longer have these remove automatically when you quit Safari. Fortunately, Firefox still does. I just have to periodically click the "Remove All Website Data" in Safari. I do a lot of testing and like to have the browsers cleared of *anything* that might be cached.
And if you mean the IndexedDB:
Maybe these articles by the folks from Sitepoint will help?
or Safari's version of it called Web SQL Database
So, if you start designing for either you may run into "not supported, or partially supported" in various browsers.
"Standards" are NOT....
Yeah, my fiancee panicked when she got a warning from Safari about Google Mail wanting an additional 5 MB of storage for the database it uses. We had to research what these were and what they were used for. Kind of a pain, really; Safari throws up the warning without explaining what it is, which makes people think it's a trojan or something else that might represent a security risk.
Worst part is, the blasted thing fills up and won't go away - which means the warning will continue popping up until you either give it more space or delete it. And it will eventually come back when it fills up again.