Several improvements to escape sequence handling.

* Add the missing special character \_ (underscore).
* Partial implementations of \a (leader character)
and \E (uninterpreted escape character).
* Parse and ignore \r (reverse line feed).
* Add a WARNING message about undefined escape sequences.
* Add an UNSUPP message about unsupported escape sequences.
* Mark \! and \? (transparent throughput)
and \O (suppress output) as unsupported.
* Treat the various variants of zero-width spaces as one-byte escape
sequences rather than as special characters, to avoid defining bogus
forms with square brackets.
* For special characters with one-byte names, do not define bogus
forms with square brackets, except for \[-], which is valid.
* In the form with square brackets, undefined special characters do not
fall back to printing the name verbatim, not even for one-byte names.
* Starting a special character name with a blank is an error.
* Undefined escape sequences never abort formatting of the input
string, not even in HTML output mode.
* Document the newly handled escapes, and a few that were missing.
* Regression tests for most of the above.

27 files changed, 303 insertions, 58 deletions

diff --git a/regress/char/accent/Makefile b/regress/char/accent/Makefile
index 4bc149a7..3712217e 100644
--- a/regress/char/accent/Makefile
+++ b/regress/char/accent/Makefile
@@ -3,5 +3,6 @@
 REGRESS_TARGETS = nocombine utf8only combine
 SKIP_ASCII = utf8only combine
 UTF8_TARGETS = nocombine utf8only combine
+LINT_TARGETS = nocombine
 
 .include <bsd.regress.mk>
diff --git a/regress/char/accent/nocombine.in b/regress/char/accent/nocombine.in
index a81d446b..637d337e 100644
--- a/regress/char/accent/nocombine.in
+++ b/regress/char/accent/nocombine.in
@@ -1,17 +1,17 @@
 .\" $OpenBSD: nocombine.in,v 1.2 2017/07/04 14:53:23 schwarze Exp $
-.TH CHAR-ACCENT-NOCOMBINE 1 "March 8, 2014"
+.TH CHAR-ACCENT-NOCOMBINE 1 "December 15, 2018"
 .SH NAME
 \fBchar-accent-nocombine\fR - non-combining accents
 .SH DESCRIPTION
 bare acute accent: e'e
 .br
-escaped acute accent: e\'e
+escaped acute accent: e\'e\[']e
 .br
 acute accent sequence: e\(aae
 .br
 bare grave accent: e`e
 .br
-escaped grave accent: e\`e
+escaped grave accent: e\`e\[`]e
 .br
 acute grave sequence: e\(gae
 .br
@@ -20,15 +20,15 @@ hungarian umlaut: e\(a"e
 .\" XXX This is ridiculous.
 .\" XXX groff prints the macron as an underscore in the previous line.
 .\" macron: e\(a-e
-.br
+.\" .br
 .\" XXX groff doesn't have a dot in ASCII mode, only in UTF-8 mode.
 .\" dotted: e\(a.e
-.br
+.\" .br
 circumflex: e\(a^e
 .br
 .\" XXX groff uses a backspace for this one in ASCII mode.
 .\" breve: e\(abe
-.br
+.\" .br
 cedilla: e\(ace
 .br
 dieresis: e\(ade
diff --git a/regress/char/accent/nocombine.out_ascii b/regress/char/accent/nocombine.out_ascii
index bc1cce15..0f18ac4a 100644
--- a/regress/char/accent/nocombine.out_ascii
+++ b/regress/char/accent/nocombine.out_ascii
@@ -7,10 +7,10 @@ NNAAMMEE
 
 DDEESSCCRRIIPPTTIIOONN
        bare acute accent: e'e
-       escaped acute accent: e'e
+       escaped acute accent: e'ee
        acute accent sequence: e'e
        bare grave accent: e`e
-       escaped grave accent: e`e
+       escaped grave accent: e`ee
        acute grave sequence: e`e
        hungarian umlaut: e"e
        circumflex: e^e
@@ -25,4 +25,4 @@ DDEESSCCRRIIPPTTIIOONN
 
 
 
-OpenBSD                          March 8, 2014        CHAR-ACCENT-NOCOMBINE(1)
+OpenBSD                        December 15, 2018      CHAR-ACCENT-NOCOMBINE(1)
diff --git a/regress/char/accent/nocombine.out_lint b/regress/char/accent/nocombine.out_lint
new file mode 100644
index 00000000..c9de4162
--- /dev/null
+++ b/regress/char/accent/nocombine.out_lint
@@ -0,0 +1,2 @@
+mandoc: nocombine.in:8:27: WARNING: invalid escape sequence: \[']
+mandoc: nocombine.in:14:27: WARNING: invalid escape sequence: \[`]
diff --git a/regress/char/accent/nocombine.out_utf8 b/regress/char/accent/nocombine.out_utf8
index 3aa441a2..497bf6fd 100644
--- a/regress/char/accent/nocombine.out_utf8
+++ b/regress/char/accent/nocombine.out_utf8
@@ -7,10 +7,10 @@ NNAAMMEE
 
 DDEESSCCRRIIPPTTIIOONN
        bare acute accent: e'e
-       escaped acute accent: e´e
+       escaped acute accent: e´ee
        acute accent sequence: e´e
        bare grave accent: e`e
-       escaped grave accent: e`e
+       escaped grave accent: e`ee
        acute grave sequence: e`e
        hungarian umlaut: e˝e
        circumflex: e^e
@@ -25,4 +25,4 @@ DDEESSCCRRIIPPTTIIOONN
 
 
 
-OpenBSD                          March 8, 2014        CHAR-ACCENT-NOCOMBINE(1)
+OpenBSD                        December 15, 2018      CHAR-ACCENT-NOCOMBINE(1)
diff --git a/regress/char/space/Makefile b/regress/char/space/Makefile
index b6095de3..50c81c4a 100644
--- a/regress/char/space/Makefile
+++ b/regress/char/space/Makefile
@@ -3,11 +3,12 @@
 REGRESS_TARGETS  = leading-mdoc leading-man multiple trailing-mdoc zerowidth
 REGRESS_TARGETS += eos eos-man break nobreak
 REGRESS_TARGETS += tab tab-man esct-mdoc esct-man
+REGRESS_TARGETS += invalid
 
 UTF8_TARGETS	 = zerowidth
 
 HTML_TARGETS	 = zerowidth
 
-LINT_TARGETS	 = trailing-mdoc tab tab-man esct-mdoc esct-man
+LINT_TARGETS	 = trailing-mdoc tab tab-man esct-mdoc esct-man invalid
 
 .include <bsd.regress.mk>
diff --git a/regress/char/space/esct-man.in b/regress/char/space/esct-man.in
index e7afeefe..f290d9e2 100644
--- a/regress/char/space/esct-man.in
+++ b/regress/char/space/esct-man.in
@@ -1,5 +1,5 @@
 .\" $OpenBSD: esct-man.in,v 1.2 2017/07/04 14:53:23 schwarze Exp $
-.TH SPACE-ESCT-MAN 1 2013-06-20
+.TH SPACE-ESCT-MAN 1 "December 15, 2018"
 .SH NAME
 SPACE-T-MAN \- the t escape sequence in pages with man macros
 .SH DESCRIPTION
@@ -9,10 +9,14 @@ single	tab
 .br
 single\tescape-t
 .br
+single\aescape-a
+.br
 double		tab
 .br
 double\t\tescape-t
 .br
+double\a\aescape-a
+.br
 \tThis line starts with escape-t and comes close to the right margin.
 \tThe next line starts with escape-t as well.
 .sp
@@ -20,8 +24,10 @@ In a literal display:
 .nf
 single	tab
 single\tescape-t
+single\aescape-a
 double		tab
 double\t\tescape-t
+double\a\aescape-a
 .fi
 .sp
 After the IP macro:
@@ -29,7 +35,13 @@ After the IP macro:
 text
 .IP single\tescape-t 3n
 text
+.\" XXX not implemented
+.\" .IP single\aescape-a 3n
+.\" text
 .PP
 After font macros:
 .br
 .B single\ttab
+.\" XXX not implemented
+.\" .br
+.\" .B single\aleader
diff --git a/regress/char/space/esct-man.out_ascii b/regress/char/space/esct-man.out_ascii
index 29fbabea..3056cc72 100644
--- a/regress/char/space/esct-man.out_ascii
+++ b/regress/char/space/esct-man.out_ascii
@@ -9,16 +9,20 @@ DDEESSCCRRIIPPTTIIOONN
        In plain text:
        single    tab
        singleescape-t
+       singleescape-a
        double         tab
        doubleescape-t
+       doubleescape-a
        This line starts with escape-t and comes close to the right margin.
        The next line starts with escape-t as well.
 
        In a literal display:
        single    tab
        singleescape-t
+       singleescape-a
        double         tab
        doubleescape-t
+       doubleescape-a
 
        After the IP macro:
 
@@ -33,4 +37,4 @@ DDEESSCCRRIIPPTTIIOONN
 
 
 
-OpenBSD                           2013-06-20                 SPACE-ESCT-MAN(1)
+OpenBSD                        December 15, 2018             SPACE-ESCT-MAN(1)
diff --git a/regress/char/space/esct-man.out_lint b/regress/char/space/esct-man.out_lint
index c625b3a3..2fa8ba9c 100644
--- a/regress/char/space/esct-man.out_lint
+++ b/regress/char/space/esct-man.out_lint
@@ -1,6 +1,6 @@
 mandoc: esct-man.in:8:7: WARNING: tab in filled text
-mandoc: esct-man.in:12:7: WARNING: tab in filled text
-mandoc: esct-man.in:12:8: WARNING: tab in filled text
-mandoc: esct-man.in:28:11: WARNING: tab in filled text
-mandoc: esct-man.in:30:11: WARNING: tab in filled text
-mandoc: esct-man.in:35:10: WARNING: tab in filled text
+mandoc: esct-man.in:14:7: WARNING: tab in filled text
+mandoc: esct-man.in:14:8: WARNING: tab in filled text
+mandoc: esct-man.in:34:11: WARNING: tab in filled text
+mandoc: esct-man.in:36:11: WARNING: tab in filled text
+mandoc: esct-man.in:44:10: WARNING: tab in filled text
diff --git a/regress/char/space/invalid.in b/regress/char/space/invalid.in
new file mode 100644
index 00000000..c4692453
--- /dev/null
+++ b/regress/char/space/invalid.in
@@ -0,0 +1,15 @@
+.\" $OpenBSD$
+.TH SPACE-INVALID 1 "December 15, 2018"
+.SH NAME
+SPACE-INVALID \- invalid whitespace escape sequences
+.SH DESCRIPTION
+.nf
+blank: a\[hy]b\[ hy]c
+percent: a\%b\[%]c
+ampersand: a\&b\[&]c
+colon: a\:b\[:]c
+caret: a\^b\[^]c
+underline: a\_b\[_]c
+pipe: a\|b\[|]c
+tilde: a\~b\[~]c
+digit-width: a\0b\[0]c
diff --git a/regress/char/space/invalid.out_ascii b/regress/char/space/invalid.out_ascii
new file mode 100644
index 00000000..bf3b5a16
--- /dev/null
+++ b/regress/char/space/invalid.out_ascii
@@ -0,0 +1,21 @@
+SPACE-INVALID(1)            General Commands Manual           SPACE-INVALID(1)
+
+
+
+NNAAMMEE
+       SPACE-INVALID - invalid whitespace escape sequences
+
+DDEESSCCRRIIPPTTIIOONN
+       blank: a-bhy]c
+       percent: abc
+       ampersand: abc
+       colon: abc
+       caret: abc
+       underline: a_bc
+       pipe: abc
+       tilde: a bc
+       digit-width: a bc
+
+
+
+OpenBSD                        December 15, 2018              SPACE-INVALID(1)
diff --git a/regress/char/space/invalid.out_lint b/regress/char/space/invalid.out_lint
new file mode 100644
index 00000000..c05ef38f
--- /dev/null
+++ b/regress/char/space/invalid.out_lint
@@ -0,0 +1,9 @@
+mandoc: invalid.in:7:15: WARNING: invalid escape sequence: \[ 
+mandoc: invalid.in:8:14: WARNING: invalid escape sequence: \[%]
+mandoc: invalid.in:9:16: WARNING: invalid escape sequence: \[&]
+mandoc: invalid.in:10:12: WARNING: invalid escape sequence: \[:]
+mandoc: invalid.in:11:12: WARNING: invalid escape sequence: \[^]
+mandoc: invalid.in:12:16: WARNING: invalid escape sequence: \[_]
+mandoc: invalid.in:13:11: WARNING: invalid escape sequence: \[|]
+mandoc: invalid.in:14:12: WARNING: invalid escape sequence: \[~]
+mandoc: invalid.in:15:18: WARNING: invalid escape sequence: \[0]
diff --git a/regress/roff/esc/Makefile b/regress/roff/esc/Makefile
index 32589479..74f153d5 100644
--- a/regress/roff/esc/Makefile
+++ b/regress/roff/esc/Makefile
@@ -1,6 +1,7 @@
 # $OpenBSD: Makefile,v 1.11 2015/04/29 18:32:57 schwarze Exp $
 
-REGRESS_TARGETS = one two multi B c c_man e f h l o p w z ignore
-LINT_TARGETS	= B h l w ignore
+REGRESS_TARGETS	 = one two multi B c c_man e f h l O o p w z
+REGRESS_TARGETS	+= ignore invalid unsupp
+LINT_TARGETS	 = B h l O w ignore invalid unsupp
 
 .include <bsd.regress.mk>
diff --git a/regress/roff/esc/O.in b/regress/roff/esc/O.in
new file mode 100644
index 00000000..d446ebb6
--- /dev/null
+++ b/regress/roff/esc/O.in
@@ -0,0 +1,15 @@
+.\" $OpenBSD$
+.TH ESC-O 1 "December 15, 2018"
+.SH NAME
+esc-O \- escape sequence to suppress output
+.SH DESCRIPTION
+.nf
+O1: a\O1b
+O2: a\O2b
+O3: a\O3b
+O4: a\O4b
+O5: a\O5b
+O52: a\O(52b
+O5n: a\O[5dummy]b
+O6: a\O6b
+O0: a\O0\&\O1b
diff --git a/regress/roff/esc/O.out_ascii b/regress/roff/esc/O.out_ascii
new file mode 100644
index 00000000..d2e5668c
--- /dev/null
+++ b/regress/roff/esc/O.out_ascii
@@ -0,0 +1,21 @@
+ESC-O(1)                    General Commands Manual                   ESC-O(1)
+
+
+
+NNAAMMEE
+       esc-O - escape sequence to suppress output
+
+DDEESSCCRRIIPPTTIIOONN
+       O1: ab
+       O2: ab
+       O3: ab
+       O4: ab
+       O5: ab
+       O52: ab
+       O5n: ab
+       O6: ab
+       O0: ab
+
+
+
+OpenBSD                        December 15, 2018                      ESC-O(1)
diff --git a/regress/roff/esc/O.out_lint b/regress/roff/esc/O.out_lint
new file mode 100644
index 00000000..ee91008d
--- /dev/null
+++ b/regress/roff/esc/O.out_lint
@@ -0,0 +1,5 @@
+mandoc: O.in:11:6: WARNING: invalid escape sequence: \O5
+mandoc: O.in:12:7: WARNING: invalid escape sequence: \O(52
+mandoc: O.in:13:7: UNSUPP: unsupported escape sequence: \O[5dummy]
+mandoc: O.in:14:6: WARNING: invalid escape sequence: \O6
+mandoc: O.in:15:6: UNSUPP: unsupported escape sequence: \O0
diff --git a/regress/roff/esc/ignore.in b/regress/roff/esc/ignore.in
index 6ba7cccc..48507f44 100644
--- a/regress/roff/esc/ignore.in
+++ b/regress/roff/esc/ignore.in
@@ -1,15 +1,13 @@
 .\" $OpenBSD: ignore.in,v 1.3 2017/07/04 14:53:27 schwarze Exp $
-.Dd $Mdocdate$
-.Dt ESC-IGNORE 1
-.Os
-.Sh NAME
-.Nm esc-ignore
-.Nd ignored roff escape sequences
-.Sh DESCRIPTION
+.TH ESC-IGNORE 1 "December 15, 2018"
+.SH NAME
+esc-ignore \- ignored roff escape sequences
+.SH DESCRIPTION
+.nf
+closing parenthesis: a\)b\[)]c
+comma: a\,b\[,]c
+slash: a\/b\[/]c
 multiform: a\kxb\k(xyc\k[xyz]d
-.br
 quoted: a\R'myreg 0'b\R'myreg \A'y'0'c
-.br
 sizes: a\s0b\s(12c\s[123]d\s'123'e\s'1\w'xy'2'f
-.br
 signed sizes: a\s-0b\s-(12c\s-[123]d\s-'123'e\s-'1\w'xy'2'f\s-
diff --git a/regress/roff/esc/ignore.out_ascii b/regress/roff/esc/ignore.out_ascii
index fa16f389..eaee36c0 100644
--- a/regress/roff/esc/ignore.out_ascii
+++ b/regress/roff/esc/ignore.out_ascii
@@ -1,12 +1,19 @@
 ESC-IGNORE(1)               General Commands Manual              ESC-IGNORE(1)
 
+
+
 NNAAMMEE
-     eesscc--iiggnnoorree - ignored roff escape sequences
+       esc-ignore - ignored roff escape sequences
 
 DDEESSCCRRIIPPTTIIOONN
-     multiform: abcd
-     quoted: abc
-     sizes: abcdef
-     signed sizes: abcdef
+       closing parenthesis: abc
+       comma: abc
+       slash: abc
+       multiform: abcd
+       quoted: abc
+       sizes: abcdef
+       signed sizes: abcdef
+
+
 
-OpenBSD                          July 4, 2017                          OpenBSD
+OpenBSD                        December 15, 2018                 ESC-IGNORE(1)
diff --git a/regress/roff/esc/ignore.out_lint b/regress/roff/esc/ignore.out_lint
index 95eba933..0f33c929 100644
--- a/regress/roff/esc/ignore.out_lint
+++ b/regress/roff/esc/ignore.out_lint
@@ -1 +1,4 @@
-mandoc: ignore.in:15:60: WARNING: invalid escape sequence: \s-
+mandoc: ignore.in:7:26: WARNING: invalid escape sequence: \[)]
+mandoc: ignore.in:8:12: WARNING: invalid escape sequence: \[,]
+mandoc: ignore.in:9:12: WARNING: invalid escape sequence: \[/]
+mandoc: ignore.in:13:60: WARNING: invalid escape sequence: \s-
diff --git a/regress/roff/esc/invalid.in b/regress/roff/esc/invalid.in
new file mode 100644
index 00000000..b2e77159
--- /dev/null
+++ b/regress/roff/esc/invalid.in
@@ -0,0 +1,28 @@
+.\" $OpenBSD$
+.TH ESC-INVALID 1 "December 15, 2018"
+.SH NAME
+esc-invalid \- invalid roff escape sequences
+.SH DESCRIPTION
+.nf
+plus: a\+b\[+]c
+semicolon: a\;b\[;]c
+less than: a\<b\[<]c
+equal to: a\=b\[=]c
+greater than: a\>b\[>]c
+at: a\@b\[@]c
+square bracket: a\]b
+curly braces: a\[{]b\[}]c
+digit: a\1b\[1]c
+G: a\Gb\[G]c
+I: a\Ib\[I]c
+i: a\ib\[i]c
+J: a\Jb\[J]c
+j: a\jb\[j]c
+K: a\Kb\[K]c
+P: a\Pb\[P]c
+Q: a\Qb\[Q]c
+q: a\qb\[q]c
+T: a\Tb\[T]c
+U: a\Ub\[U]c
+W: a\Wb\[W]c
+y: a\yb\[y]c
diff --git a/regress/roff/esc/invalid.out_ascii b/regress/roff/esc/invalid.out_ascii
new file mode 100644
index 00000000..24915262
--- /dev/null
+++ b/regress/roff/esc/invalid.out_ascii
@@ -0,0 +1,34 @@
+ESC-INVALID(1)              General Commands Manual             ESC-INVALID(1)
+
+
+
+NNAAMMEE
+       esc-invalid - invalid roff escape sequences
+
+DDEESSCCRRIIPPTTIIOONN
+       plus: a+bc
+       semicolon: a;bc
+       less than: a<bc
+       equal to: a=bc
+       greater than: a>bc
+       at: a@bc
+       square bracket: a]b
+       curly braces: abc
+       digit: a1bc
+       G: aGbc
+       I: aIbc
+       i: aibc
+       J: aJbc
+       j: ajbc
+       K: aKbc
+       P: aPbc
+       Q: aQbc
+       q: aqbc
+       T: aTbc
+       U: aUbc
+       W: aWbc
+       y: aybc
+
+
+
+OpenBSD                        December 15, 2018                ESC-INVALID(1)
diff --git a/regress/roff/esc/invalid.out_lint b/regress/roff/esc/invalid.out_lint
new file mode 100644
index 00000000..a0afa7ae
--- /dev/null
+++ b/regress/roff/esc/invalid.out_lint
@@ -0,0 +1,43 @@
+mandoc: invalid.in:7:11: WARNING: invalid escape sequence: \[+]
+mandoc: invalid.in:7:8: WARNING: undefined escape, printing literally: \+
+mandoc: invalid.in:8:16: WARNING: invalid escape sequence: \[;]
+mandoc: invalid.in:8:13: WARNING: undefined escape, printing literally: \;
+mandoc: invalid.in:9:16: WARNING: invalid escape sequence: \[<]
+mandoc: invalid.in:9:13: WARNING: undefined escape, printing literally: \<
+mandoc: invalid.in:10:15: WARNING: invalid escape sequence: \[=]
+mandoc: invalid.in:10:12: WARNING: undefined escape, printing literally: \=
+mandoc: invalid.in:11:19: WARNING: invalid escape sequence: \[>]
+mandoc: invalid.in:11:16: WARNING: undefined escape, printing literally: \>
+mandoc: invalid.in:12:9: WARNING: invalid escape sequence: \[@]
+mandoc: invalid.in:12:6: WARNING: undefined escape, printing literally: \@
+mandoc: invalid.in:13:18: WARNING: undefined escape, printing literally: \]
+mandoc: invalid.in:14:21: WARNING: invalid escape sequence: \[}]
+mandoc: invalid.in:14:16: WARNING: invalid escape sequence: \[{]
+mandoc: invalid.in:15:12: WARNING: invalid escape sequence: \[1]
+mandoc: invalid.in:15:9: WARNING: undefined escape, printing literally: \1
+mandoc: invalid.in:16:8: WARNING: invalid escape sequence: \[G]
+mandoc: invalid.in:16:5: WARNING: undefined escape, printing literally: \G
+mandoc: invalid.in:17:8: WARNING: invalid escape sequence: \[I]
+mandoc: invalid.in:17:5: WARNING: undefined escape, printing literally: \I
+mandoc: invalid.in:18:8: WARNING: invalid escape sequence: \[i]
+mandoc: invalid.in:18:5: WARNING: undefined escape, printing literally: \i
+mandoc: invalid.in:19:8: WARNING: invalid escape sequence: \[J]
+mandoc: invalid.in:19:5: WARNING: undefined escape, printing literally: \J
+mandoc: invalid.in:20:8: WARNING: invalid escape sequence: \[j]
+mandoc: invalid.in:20:5: WARNING: undefined escape, printing literally: \j
+mandoc: invalid.in:21:8: WARNING: invalid escape sequence: \[K]
+mandoc: invalid.in:21:5: WARNING: undefined escape, printing literally: \K
+mandoc: invalid.in:22:8: WARNING: invalid escape sequence: \[P]
+mandoc: invalid.in:22:5: WARNING: undefined escape, printing literally: \P
+mandoc: invalid.in:23:8: WARNING: invalid escape sequence: \[Q]
+mandoc: invalid.in:23:5: WARNING: undefined escape, printing literally: \Q
+mandoc: invalid.in:24:8: WARNING: invalid escape sequence: \[q]
+mandoc: invalid.in:24:5: WARNING: undefined escape, printing literally: \q
+mandoc: invalid.in:25:8: WARNING: invalid escape sequence: \[T]
+mandoc: invalid.in:25:5: WARNING: undefined escape, printing literally: \T
+mandoc: invalid.in:26:8: WARNING: invalid escape sequence: \[U]
+mandoc: invalid.in:26:5: WARNING: undefined escape, printing literally: \U
+mandoc: invalid.in:27:8: WARNING: invalid escape sequence: \[W]
+mandoc: invalid.in:27:5: WARNING: undefined escape, printing literally: \W
+mandoc: invalid.in:28:8: WARNING: invalid escape sequence: \[y]
+mandoc: invalid.in:28:5: WARNING: undefined escape, printing literally: \y
diff --git a/regress/roff/esc/one.in b/regress/roff/esc/one.in
index 910714d1..6a4b22a8 100644
--- a/regress/roff/esc/one.in
+++ b/regress/roff/esc/one.in
@@ -1,17 +1,11 @@
 .\" $OpenBSD: one.in,v 1.3 2017/07/04 14:53:27 schwarze Exp $
-.Dd $Mdocdate$
-.Dt ESC-ONE 1
-.Os
-.Sh NAME
-.Nm esc-one
-.Nd roff one-character escape sequences
-.Sh DESCRIPTION
+.TH ESC-ONE 1 "December 15, 2018"
+.SH NAME
+esc-one \- roff one-character escape sequences
+.SH DESCRIPTION
+.nf
 backslash: >\e<
-.br
-minus: >\-<
-.br
+minus: >\-|\[-]<
 acute: >\'<
-.br
 grave: >\`<
-.br
 normal character: >\q<
diff --git a/regress/roff/esc/one.out_ascii b/regress/roff/esc/one.out_ascii
index bc88dcf2..1eb5f1f2 100644
--- a/regress/roff/esc/one.out_ascii
+++ b/regress/roff/esc/one.out_ascii
@@ -1,13 +1,17 @@
 ESC-ONE(1)                  General Commands Manual                 ESC-ONE(1)
 
+
+
 NNAAMMEE
-     eesscc--oonnee - roff one-character escape sequences
+       esc-one - roff one-character escape sequences
 
 DDEESSCCRRIIPPTTIIOONN
-     backslash: >\<
-     minus: >-<
-     acute: >'<
-     grave: >`<
-     normal character: >q<
+       backslash: >\<
+       minus: >-|-<
+       acute: >'<
+       grave: >`<
+       normal character: >q<
+
+
 
-OpenBSD                          July 4, 2017                          OpenBSD
+OpenBSD                        December 15, 2018                    ESC-ONE(1)
diff --git a/regress/roff/esc/unsupp.in b/regress/roff/esc/unsupp.in
new file mode 100644
index 00000000..819f6c33
--- /dev/null
+++ b/regress/roff/esc/unsupp.in
@@ -0,0 +1,8 @@
+.\" $OpenBSD$
+.TH ESC-UNSUPP 1 "December 15, 2018"
+.SH NAME
+esc-unsupp \- unsupported escape sequences
+.SH DESCRIPTION
+.nf
+exclamation mark: a\!b\[!]c
+question mark: a\?\&\?b\[?]c
diff --git a/regress/roff/esc/unsupp.out_ascii b/regress/roff/esc/unsupp.out_ascii
new file mode 100644
index 00000000..22613e54
--- /dev/null
+++ b/regress/roff/esc/unsupp.out_ascii
@@ -0,0 +1,14 @@
+ESC-UNSUPP(1)               General Commands Manual              ESC-UNSUPP(1)
+
+
+
+NNAAMMEE
+       esc-unsupp - unsupported escape sequences
+
+DDEESSCCRRIIPPTTIIOONN
+       exclamation mark: abc
+       question mark: abc
+
+
+
+OpenBSD                        December 15, 2018                 ESC-UNSUPP(1)
diff --git a/regress/roff/esc/unsupp.out_lint b/regress/roff/esc/unsupp.out_lint
new file mode 100644
index 00000000..d3cc4bf1
--- /dev/null
+++ b/regress/roff/esc/unsupp.out_lint
@@ -0,0 +1,5 @@
+mandoc: unsupp.in:7:23: WARNING: invalid escape sequence: \[!]
+mandoc: unsupp.in:7:20: UNSUPP: unsupported escape sequence: \!
+mandoc: unsupp.in:8:24: WARNING: invalid escape sequence: \[?]
+mandoc: unsupp.in:8:21: UNSUPP: unsupported escape sequence: \?
+mandoc: unsupp.in:8:17: UNSUPP: unsupported escape sequence: \?