| Value | Meaning |
|---|---|
| http | http:// protocol absolute links |
| https | https:// protocol absolute links |
| data | data: url links to embed content. On some browsers (old Firefoxes) this was a security concern. |
| ftp | ftp:// protocol links |
| relative | relative links to the current location. You might want to rebase them. |
| anchors | #anchor links |
The things to allow in links, images, css, and aother urls. FIXME: implement this for better flexibility