What web protocols are possible for a CSS background image url?

Question

I am creating an application for which it is required str_replace()for any lines http:or https:in the URL of a background image. Does anyone know of any other protocols that are possible for the background image url? For example, are any of the following methods possible, or did anyone see a CSS image in the URL of any of the following elements?

TCP
UDP
ICMP
POP
FTP
IMAP

As one example, is this possible for CSS?

#myDiv {    background-image: URL("ftps://mysite.com/pub/myimage.png");    }

Thank you for understanding!

Answer 1

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TCP, UDP ICMP - , , ftp, pop imap . . : https://en.wikipedia.org/wiki/URI_scheme

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Answer 2

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CSS2, , , URI RFC3986, CSS1.

URI , , URI ( ..).

, - : , CSS , .

, , HTTPS CSS1- , CSS1 RFC HTTPS.