Split the excessively generic diagnostic message "invalid escape sequence"

into the more specific messages "invalid escape argument delimiter"
and "invalid escape sequence argument".

1 files changed, 14 insertions, 3 deletions

diff --git a/mandoc.1 b/mandoc.1
index c9d59ccc..e01a103c 100644
--- a/mandoc.1
+++ b/mandoc.1
@@ -1797,10 +1797,9 @@ it is hard to predict which tab stop position the tab will advance to.
 .Pq mdoc
 A new sentence starts in the middle of a text line.
 Start it on a new input line to help formatters produce correct spacing.
-.It Sy "invalid escape sequence"
+.It Sy "invalid escape sequence argument"
 .Pq roff
-An escape sequence has an invalid opening argument delimiter
-or the argument is of an invalid form.
+The argument of an escape sequence is of an invalid form.
 Invalid escape sequences are ignored.
 .It Sy "undefined escape, printing literally"
 .Pq roff
@@ -2314,6 +2313,18 @@ The escape sequence is ignored.
 The name given in a special character escape sequence is not known to
 .Nm .
 The escape sequence is ignored.
+.It Sy "invalid escape argument delimiter"
+.Pq roff
+An escape sequence that expects a numerical argument
+attempts to employ one of the characters
+.Qq " %&()*+-./0123456789:<=>"
+as an argument delimiter.
+The escape sequence is ignored including the invalid opening delimiter
+and the rest of the argument may appear as output text.
+While various charcters can be used as argument delimiters,
+using the apostrophe-quote character
+.Pq Sq \(aq
+is recommended for readability and robustness.
 .El
 .Ss Unsupported features
 .Bl -ohang