doc: codify optional alternatives notation.

* txr.1: The notation [ a | b | c | .. ] is used throughout
the document, but the Conventions paragraph describes only
square brackets around a single optional element. The notation
is now officially codified.

1 files changed, 7 insertions, 1 deletions

diff --git a/txr.1 b/txr.1
index 6d89ea01..60b36805 100644
--- a/txr.1
+++ b/txr.1
@@ -14097,7 +14097,8 @@ The curly braces may be omitted if the scope of the
 is clear.
 
 .coIP {syntax | syntax | ...}
-This indicates a choice among alternatives.
+This indicates a single, mandatory element, which is selected
+from among the indicated alternatives.
 May be combined with
 .code +
 or
@@ -14107,6 +14108,11 @@ repetition.
 .meIP [syntax] <> [ word ]
 Square brackets indicate optional syntax.
 
+.meIP [syntax | syntax | ...]
+Square brackets containing piped elements indicate an optional
+element, which, if present, must be chosen from among the indicated
+alternatives.
+
 .coIP '[' ']'
 The quoted square brackets indicate literal brackets which appear
 in the syntax, which they do without quotes. For instance