+\S2{plink-option-s} \I{-s-plink}\c{-s}: remote command is SSH subsystem
+
+If you specify the \c{-s} option, Plink passes the specified command
+as the name of an SSH \q{\i{subsystem}} rather than an ordinary command
+line.
+
+(This option is only meaningful with the SSH-2 protocol.)
+
+\S2{plink-option-shareexists} \I{-shareexists-plink}\c{-shareexists}:
+test for connection-sharing upstream
+
+This option does not make a new connection; instead it allows testing
+for the presence of an existing connection that can be shared.
+(See \k{config-ssh-sharing} for more information about SSH connection
+sharing.)
+
+A Plink invocation of the form:
+
+\c plink -shareexists <session>
+\e iiiiiiiii
+
+will test whether there is currently a viable \q{upstream} for the
+session in question, which can be specified using any syntax you'd
+normally use with Plink to make an actual connection (a host/port
+number, a bare saved session name, \c{-load}, etc). It returns a
+zero exit status if a usable \q{upstream} exists, nonzero otherwise.
+
+(This option is only meaningful with the SSH-2 protocol.)
+