Quoting from the XTerm documentation:
The first, Pc, may contain zero or more characters from the set c, p, q,
s, 0, 1, 2, 3, 4, 5, 6, and 7. It is used to construct a list of
selection parameters for clipboard, primary, secondary, select, or
cut-buffers 0 through 7 respectively, in the order given. If the
parameter is empty, xterm uses s 0 , to specify the configurable
primary/clipboard selection and cut-buffer 0.
See https://invisible-island.net/xterm/ctlseqs/ctlseqs.html
This adds support for OSC 52 -- applications can read/write the clipboard. Due to the security risk of this, the default configuration allows for writing but _not reading_. This is configurable using two new settings: `clipboard-read` and `clipboard-write` (both booleans).
