It’s based on xclip() or xsel() that require X11 implementation

xclip.c has its own functions:

• *get_requestor,
• del_requestor,
• clean_requestors,
• doOptMain,
• doOptSel,
• doOptTarget,
• doIn,
• printSelBuf,
• doOut

xsel.c functions:

• get_atom_name
• debug_property
• xs_malloc
• _xs_strdup
• _xs_strncpy
• get_xdg_cache_home
• block_exit_sigs
• unblock_exit_sigs
• alarm_handler
• and other (about 49 more)

Linux Clipboard itself is based on freedesktop.org

Repositories: pyperclip, xclip, xsel
Found: Michael Butscher, Some Programmer Dude, Håkon Hægland