Abbreviated long options on the command line of xclip

In the manpage of xclip -selection specify which X selection to use, options are "primary" to use XA_PRIMARY (default), "secondary" for XA_SECONDARY or "clipboard" for XA_CLIPBOARD Note that only the first character of the selection specified with the -selection option is important. This means that "p", "sec" and "clip" would have the same effect as using "primary", "secondary" or "clipboard" respectively. The following for using clipboard selection works xclip -sel clip < ~/.ssh/id_rsa.pub the manpage says that clipboard can be shortened to clip, but doesn't say that -selection can be shortened to -sel. So why does it work? Does this feature for specifying an option belong to xclip, or also to many other applications besides xclip?