OSC52 is a terminal escape sequence that allows copying text to the clipboard.
The sequence consists of the following:
Pc is the clipboard choice:
Pd is the data to copy to the clipboard. This string should be encoded in
base64 (RFC-4648).
If Pd is "?", the terminal replies to the host with the current contents of
the clipboard.
If Pd is neither a base64 string nor "?", the terminal clears the clipboard.
See https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Operating-System-Commands
where Ps = 52 => Manipulate Selection Data.