X:
URL scheme[2] Federal Information Processing Standards Publication: X window system version 11 release 5 (X window system protocol; Xlib-C langauge X interface; X toolkit intrinsics - C language interface; bitmap distribution format 2.1) - fipspub158-1.pdf, , https://nvlpubs.nist.gov/nistpubs/Legacy/FIPS/fipspub158-1.pdf