Only Tty reads Word+arg as its argument

Every builtin that takes an argument split a word at its first +, so
Dump+2024.zon ran Dump with 2024.zon. A builtin now opts in with plus_arg,
read by the registry, and only Tty does.

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

1 files changed, 4 insertions, 3 deletions

diff --git a/docs/tags.md b/docs/tags.md
index 2f68bc0d..f1d7794d 100644
--- a/docs/tags.md
+++ b/docs/tags.md
@@ -7,9 +7,10 @@ pane (or its first pane when focus comes from another column). This makes
 `New` appears only in the column tag by default; pane tags keep their own
 save, terminal, close, and collapse commands. `Tty` opens a new embedded terminal.
 In a terminal's own tag the word names the shell it runs, `Tty+fish`, tinted
-with the tag's name colour: `Word+arg` is one word a tag can hold for
-`Word arg`, so clicking it opens another terminal on that shell, as `Tty
-fish` would. A command pane's tag reads `<dir> (<line>) running` or `exit N`
+with the tag's name colour: `Tty+arg` is one word a tag can hold for `Tty
+arg`, so clicking it opens another terminal on that shell, as `Tty fish`
+would. Only a builtin that declares `plus_arg` reads a `+` so; `Tty` is the
+one, since other arguments (a dump's name) may contain `+`. A command pane's tag reads `<dir> (<line>) running` or `exit N`
 and offers `Kill`.
 Pane and column command text leave a small gap after their aligned drag grips.
 GUI pane mode symbols are centered by their visible ink; changing the font or