A pane's word written to /tagexec or a column's exec is refused, not done at the focused pane

Undo, Msg and the other pane words written to a tag no pane owns ran at
whichever pane had the keyboard. They are refused as the root's ctl
refuses them, EINVAL; the tag's own words (a column's New, Tty, Find,
Grep) still run.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 5 insertions, 1 deletions

diff --git a/docs/fs.md b/docs/fs.md
index dc3e7533..d94a1954 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -130,7 +130,11 @@ Existing Plan9port/v9fs clients need a userspace bridge for QUIC.
              tag does not move, so the two can differ -- the active column, where
              pane/new and a look place a pane next (- when there is none)
 /tag         the workspace tag; > replaces it, >> appends, one line
-/tagexec     write a word: a middle click on it in the workspace tag; read as /exec
+/tagexec     write a word: a middle click on it in the workspace tag; read as /exec. A
+             pane's word (Undo, Msg, Save) is refused there and at a column's exec,
+             `not a session control message "Undo": write it to pane/<n>/ctl` (EINVAL),
+             never done at the pane with the keyboard; a tag's own words (New, Tty,
+             Find, Grep in a column's) run
 /col/<n>/tag the tag of the column with serial n, the same way
 /col/<n>/ctl write Delcol, Joincol, New or Tty: each acts on that column, as from its tag
 /col/<n>/exec write a word: a middle click on it in that column's tag; read as /exec; rmdir col/<n> closes