From 7428e1d6af1875c337533c760c83cd7dd797fdb6 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sat, 10 Sep 2022 07:56:15 -0700
Subject: doc: document [. expr] support.

* txr.1: Document and advise users that it
doesn't work in 281 or older versions.
---
 txr.1 | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/txr.1 b/txr.1
index 1037fbc9..0f9ec8c6 100644
--- a/txr.1
+++ b/txr.1
@@ -12018,6 +12018,34 @@ or an atom
 as
 .codn "(. sym)" .
 
+This notation is implemented for the square brackets, according to this
+transformation:
+
+.verb
+  [. expr] -> (dwim . expr)
+.brev
+
+This is useful in Structural Pattern Matching, allowing a pattern like
+
+.verb
+  [. @args]
+.brev
+
+to match a
+.code dwim
+expression and capture all of its arguments in a variable, without having
+to resort to the internal notation:
+
+Compatibility Note: support for
+.code "[. expr]"
+was introduced in \*(TX 282. Older versions do not read the syntax,
+but do print
+.code "(dwim . @var)"
+as
+.code "[. @var]"
+which is then unreadable in those versions, breaking read-print
+consistency.
+
 .NP* Referencing Dot
 
 A dot token which is flanked by expressions on both sides, without any
-- 
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