implemented ncurses clipboard support via external processes

* As an alternative to OSC-52, which is rarely supported by terminal emulators.
* Makes the new mouse support much more useful since you rely on good builtin
  clipboard support. You can no longer e.g. just double-click a word to copy it into
  the "primary" selection as terminal emulators do by default.
* Set $SCITECO_CLIPBOARD_SET/GET e.g. to xclip, way-copy, pbcopy or some wrapper script.
* This is currently using POSIX-specific popen() API, so it behaves a bit different
  to command execution via EC/EG.
  I am not sure if it's worth rewriting with the GSpawn-API, since it will be used
  only on POSIX anyway and a GSpawn-based implementation is likely to be a bit larger.
* Should there be some small command-line utility for interacting (esp. pasting) via OSC-52,
  built-in OSC-52 support could well be removed from SciTECO.
  Currently, I know only of https://github.com/theimpostor/osc/ and it requires
  very recent Go compilers. (I still haven't tested it. Quite possibly, pasting when run as
  a piped command is impossible.)

1 files changed, 14 insertions, 7 deletions

diff --git a/doc/sciteco.7.template b/doc/sciteco.7.template
index 95c3503..b274715 100644
--- a/doc/sciteco.7.template
+++ b/doc/sciteco.7.template
@@ -1580,10 +1580,10 @@ The existence of a clipboard register can thus be checked
 in macros to determine whether getting and modifying that
 particular clipboard is supported natively.
 .br
+\*(ST supports two ways of driving the clipboard on ncurses.
 .SCITECO_TOPIC OSC-52 xterm
-\*(ST does \fBnot\fP generally support clipboards on ncurses,
-but has special support for OSC-52 escape sequences, as were
-introduced by sufficiently recent versions of
+First of all, there is built-in support for OSC-52 escape sequences,
+as were introduced by sufficiently recent versions of
 .BR xterm (1)
 and have since been adopted by several other terminal emulators.
 Since the operability of OSC-52 clipboards cannot be tested
@@ -1593,6 +1593,7 @@ configured.
 .BR xterm (1)
 for instance must be configured for allowing
 the \fISetSelection\fP and \fIGetSelection\fP window operations.
+It is nevertheless observed to be a very buggy and unreliable feature.
 If running under
 .BR xterm (1),
 \*(ST will still check whether the XTerm version is sufficient.
@@ -1601,10 +1602,16 @@ Other terminal emulators like Kitty may ask for permission to read the
 clipboard (\fBread-clipboard-ask\fP).
 This is not supported by \*(ST and must be disabled
 (use \fBread-clipboard\fP instead).
-.SCITECO_TOPIC xclip
-If native clipboard support is unavailable, users may
-still fall back to using external tools like \fBxclip\fP(1)
-with the \fBEC\fP command.
+.br
+Alternatively, if OSC-52 clipboards are disabled, you can set the
+\fB$SCITECO_CLIPBOARD_SET\fP and \fB$SCITECO_CLIPBOARD_GET\fP
+environment variables (or corresponding Q-Registers) to shell
+commands, that receive the clipboard
+contents on stdin and output the requested clipboard on stdout.
+This allows integrating with various windowing environments.
+See \fBENVIRONMENT\fP in
+.BR sciteco (1)
+for more details.
 .br
 Setting the string part of a clipboard register will set that
 clipboard. \*(ST will perform automatic EOL-translation according