diff --git a/datetime.go b/datetime.go
index 7d54649..55f9de0 100644
--- a/datetime.go
+++ b/datetime.go
@@ -79,7 +79,9 @@ func clockString(t time.Time) string {
 
 // offsetString renders an offset date-time, the fourth TOML kind, in the same
 // shape: no zero seconds, no trailing zeros in the fraction, and the offset
-// written as "Z" when it is zero.
+// written as "Z" when it is zero. A zone offset that is not a whole number of
+// minutes loses its seconds to this rendering, which is why Marshal refuses
+// such a value rather than writing it.
 func offsetString(t time.Time) string {
 	buf := t.AppendFormat(make([]byte, 0, 32), "2006-01-02T")
 	buf = appendClock(buf, t)
@@ -235,17 +237,21 @@ func normaliseDateTimeToken(tok string, kind dateTimeKind) string {
 
 // parseDateTime classifies and parses a bare token as a TOML date-time value.
 // It returns the decoded value (OffsetDateTime, LocalDateTime, LocalDate or
-// LocalTime) and whether the token was a date-time at all.
-func parseDateTime(tok string) (any, bool) {
+// LocalTime), whether the token was a date-time at all, and an error for a
+// token whose shape is a date-time a component of which lies outside its
+// range: an hour of 24, a day the month does not hold. Such a token is a
+// broken date-time, not some other value, so the error names it instead of
+// leaving it to the number decoder's complaint.
+func parseDateTime(tok string) (any, bool, error) {
 	if tok == "" || tok[0] < '0' || tok[0] > '9' {
-		return nil, false
+		return nil, false, nil
 	}
 	if !strings.ContainsAny(tok, "-:") {
-		return nil, false
+		return nil, false, nil
 	}
 	kind, seconds := scanDateTimeShape(tok)
 	if kind == dateTimeNone {
-		return nil, false
+		return nil, false, nil
 	}
 	norm := normaliseDateTimeToken(tok, kind)
 	switch kind {
@@ -256,7 +262,7 @@ func parseDateTime(tok string) (any, bool) {
 		}
 		t, err := time.Parse(layout, norm)
 		if err != nil {
-			return nil, false
+			return nil, false, fmt.Errorf("invalid date-time %q", tok)
 		}
 		// A zero offset carries its own anonymous location from time.Parse,
 		// while the written form is "Z" either way; normalising to UTC keeps
@@ -264,7 +270,7 @@ func parseDateTime(tok string) (any, bool) {
 		if _, off := t.Zone(); off == 0 {
 			t = t.In(time.UTC)
 		}
-		return OffsetDateTime{t}, true
+		return OffsetDateTime{t}, true, nil
 	case dateTimeLocal:
 		layout := localClockLayout
 		if seconds {
@@ -272,15 +278,15 @@ func parseDateTime(tok string) (any, bool) {
 		}
 		t, err := time.Parse(layout, norm)
 		if err != nil {
-			return nil, false
+			return nil, false, fmt.Errorf("invalid date-time %q", tok)
 		}
-		return LocalDateTime{t}, true
+		return LocalDateTime{t}, true, nil
 	case dateTimeDate:
 		t, err := time.Parse(localDateOnlyLayout, norm)
 		if err != nil {
-			return nil, false
+			return nil, false, fmt.Errorf("invalid date-time %q", tok)
 		}
-		return LocalDate{t}, true
+		return LocalDate{t}, true, nil
 	case dateTimeClock:
 		layout := localTimeClockLayout
 		if seconds {
@@ -288,11 +294,22 @@ func parseDateTime(tok string) (any, bool) {
 		}
 		t, err := time.Parse(layout, norm)
 		if err != nil {
-			return nil, false
+			return nil, false, fmt.Errorf("invalid date-time %q", tok)
 		}
-		return LocalTime{t}, true
+		return LocalTime{t}, true, nil
 	}
-	return nil, false
+	return nil, false, nil
+}
+
+// wholeMinuteOffset reports an error when the zone offset carries seconds, a
+// shape no TOML offset can hold: writing only the minutes would silently
+// shift the instant on the way back, so the encoder refuses the value rather
+// than corrupting it.
+func wholeMinuteOffset(t time.Time) error {
+	if _, off := t.Zone(); off%60 != 0 {
+		return fmt.Errorf("interpres: date-time offset of %d seconds is not a whole number of minutes, which TOML cannot write", off)
+	}
+	return nil
 }
 
 // isDateToken reports whether s is exactly a YYYY-MM-DD date, used to detect a
diff --git a/interpres_test.go b/interpres_test.go
index 78a762b..e04e77e 100644
--- a/interpres_test.go
+++ b/interpres_test.go
@@ -895,3 +895,111 @@ func TestParseCRLFDocument(t *testing.T) {
 		t.Errorf("tree = %v", tree)
 	}
 }
+
+// TestParseUnicodeEscapeBoundaries pins the scalar-value checks of \u and \U:
+// a surrogate, a value past U+10FFFF, and a sign are all rejected, and the
+// greatest scalar value parses.
+func TestParseUnicodeEscapeBoundaries(t *testing.T) {
+	bad := []struct {
+		name string
+		in   string
+	}{
+		{"high surrogate", `a = "\ud800"`},
+		{"low surrogate", `a = "\udfff"`},
+		{"past the greatest scalar", `a = "\U00110000"`},
+		{"signed short escape", `a = "\u+041"`},
+		{"negative long escape", `a = "\U-0000001"`},
+	}
+	for _, tt := range bad {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := Parse([]byte(tt.in))
+			if err == nil {
+				t.Fatalf("Parse accepted %q", tt.in)
+			}
+		})
+	}
+	tree, err := ParseMap([]byte("a = \"\\U0010FFFF\""))
+	if err != nil {
+		t.Fatalf("ParseMap: %v", err)
+	}
+	if tree["a"] != "􏿿" {
+		t.Errorf("a = %q", tree["a"])
+	}
+}
+
+// TestParseRejectsOutOfRangeDateTimes pins that a token shaped like a
+// date-time with a component out of range is rejected as a date-time, not
+// left to the number decoder's complaint.
+func TestParseRejectsOutOfRangeDateTimes(t *testing.T) {
+	bad := []struct {
+		name string
+		in   string
+	}{
+		{"hour 24", "a = 1979-05-27T24:00:00Z"},
+		{"minute 60", "a = 1979-05-27T07:60:00Z"},
+		{"second 60", "a = 1979-05-27T07:32:60Z"},
+		{"month 13", "a = 1979-13-27T07:32:00Z"},
+		{"day 32", "a = 1979-05-32T07:32:00Z"},
+		{"february the thirtieth", "a = 1979-02-30"},
+	}
+	for _, tt := range bad {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := ParseMap([]byte(tt.in))
+			if err == nil {
+				t.Fatalf("ParseMap accepted %q", tt.in)
+			}
+			if !strings.Contains(err.Error(), "invalid date-time") {
+				t.Errorf("err = %v, want the date-time complaint", err)
+			}
+		})
+	}
+}
+
+// TestParseMultilineStringEdges pins the carriage-return and delimiter rules
+// of multi-line strings: a bare CR right after the opening delimiter is the
+// bare-CR error, a CRLF pair is the trimmed newline, and a CRLF inside the
+// content survives.
+func TestParseMultilineStringEdges(t *testing.T) {
+	_, err := ParseMap([]byte("a = \"\"\"\rX\"\"\""))
+	if err == nil || !strings.Contains(err.Error(), "bare carriage return") {
+		t.Errorf("err = %v, want the bare-CR error after the delimiter", err)
+	}
+	tree, err := ParseMap([]byte("a = \"\"\"\r\nX\r\nY\"\"\""))
+	if err != nil {
+		t.Fatalf("ParseMap: %v", err)
+	}
+	if tree["a"] != "X\r\nY" {
+		t.Errorf("a = %q, want the CRLF pairs preserved", tree["a"])
+	}
+}
+
+// TestParseMultilineBasicDelimiterRuns pins that up to two extra quotes
+// before the closing delimiter of a basic multi-line string are content, and
+// more than five are the error.
+func TestParseMultilineBasicDelimiterRuns(t *testing.T) {
+	tree, err := ParseMap([]byte("a = \"\"\"end\"\"\"\""))
+	if err != nil {
+		t.Fatalf("ParseMap: %v", err)
+	}
+	if tree["a"] != `end"` {
+		t.Errorf("a = %q", tree["a"])
+	}
+	_, err = ParseMap([]byte("a = \"\"\"end\"\"\"\"\"\"\""))
+	if err == nil || !strings.Contains(err.Error(), "too many") {
+		t.Errorf("err = %v, want the too-many-delimiters error", err)
+	}
+}
+
+// TestParseLineEndingBackslashEdges pins the line-ending backslash at the
+// very end of the input and before a bare CR.
+func TestParseLineEndingBackslashEdges(t *testing.T) {
+	bad := []string{
+		"a = \"\"\"x \\\\",
+		"a = \"\"\"x \\\\\rZ\"\"\"",
+	}
+	for _, in := range bad {
+		if _, err := ParseMap([]byte(in)); err == nil {
+			t.Errorf("ParseMap accepted %q", in)
+		}
+	}
+}
diff --git a/parser.go b/parser.go
index ae05190..7435928 100644
--- a/parser.go
+++ b/parser.go
@@ -48,6 +48,13 @@ type parser struct {
 	dotted  map[string]bool
 	arrays  map[string]bool
 
+	// scopeMarks records the definition-map entries added under an array of
+	// tables, keyed by that array's path, so a new element's reset drops
+	// exactly what the previous element added. Without it the reset scans
+	// every map for the prefix, which a document with many elements and many
+	// definitions outside them turns quadratic.
+	scopeMarks map[string][]string
+
 	currentPath []string
 
 	// keys interns key strings: a document that repeats a key across
@@ -196,6 +203,7 @@ func (p *parser) markHeader(pk string) {
 		p.headers = make(map[string]bool, 4)
 	}
 	p.headers[pk] = true
+	p.trackScope(pk)
 }
 
 func (p *parser) markFrozen(pk string) {
@@ -203,6 +211,7 @@ func (p *parser) markFrozen(pk string) {
 		p.frozen = make(map[string]bool, 4)
 	}
 	p.frozen[pk] = true
+	p.trackScope(pk)
 }
 
 func (p *parser) markDotted(pk string) {
@@ -210,6 +219,7 @@ func (p *parser) markDotted(pk string) {
 		p.dotted = make(map[string]bool, 4)
 	}
 	p.dotted[pk] = true
+	p.trackScope(pk)
 }
 
 func (p *parser) markArray(pk string) {
@@ -217,6 +227,22 @@ func (p *parser) markArray(pk string) {
 		p.arrays = make(map[string]bool, 2)
 	}
 	p.arrays[pk] = true
+	p.trackScope(pk)
+}
+
+// trackScope records a definition entry under every array of tables it falls
+// inside, so resetScopeUnder can drop it when a later element opens. An entry
+// under no array, such as every definition before the first header, needs no
+// record: no reset can ever name it.
+func (p *parser) trackScope(pk string) {
+	for arr := range p.arrays {
+		if strings.HasPrefix(pk, arr+"\x00") {
+			if p.scopeMarks == nil {
+				p.scopeMarks = make(map[string][]string, 2)
+			}
+			p.scopeMarks[arr] = append(p.scopeMarks[arr], pk)
+		}
+	}
 }
 
 // internKey returns the shared string for key bytes. The lookup works on the
@@ -482,9 +508,14 @@ func (p *parser) parseKeyValue() error {
 	if p.doc != nil {
 		node := p.currentNode
 		if len(rest) > 0 {
+			// The tables a dotted key builds hold the position of a line, so
+			// the write side marks them and gives each leaf back as a dotted
+			// key rather than a header that would swallow the lines after it.
 			node = node.addTable(first, dests[0])
+			node.dotted = true
 			for i, k := range rest[:len(rest)-1] {
 				node = node.addTable(k, dests[i+1])
+				node.dotted = true
 			}
 		}
 		_, inline := val.(map[string]any)
@@ -570,25 +601,19 @@ func (p *parser) freezeInline(path []string, val any) {
 // resetScopeUnder forgets the definition records nested under key, which
 // belong to the previous element of an array of tables: headers, frozen
 // inline tables, dotted-key paths, and nested arrays of tables all start
-// fresh in the new element.
+// fresh in the new element. The records to drop are the ones the element
+// added, which scopeMarks holds; the array's own entry, and everything
+// outside it, keep their place.
 func (p *parser) resetScopeUnder(key []string) {
-	prefix := pathKey(key) + "\x00"
-	p.resetMapUnder(p.headers, prefix)
-	p.resetMapUnder(p.frozen, prefix)
-	p.resetMapUnder(p.dotted, prefix)
-	p.resetMapUnder(p.arrays, prefix)
-}
-
-// resetMapUnder deletes the entries m holds under prefix. An empty or
-// unallocated map holds none, so the common case walks nothing.
-func (p *parser) resetMapUnder(m map[string]bool, prefix string) {
-	if len(m) == 0 {
-		return
+	pk := pathKey(key)
+	for _, k := range p.scopeMarks[pk] {
+		delete(p.headers, k)
+		delete(p.frozen, k)
+		delete(p.dotted, k)
+		delete(p.arrays, k)
 	}
-	for k := range m {
-		if strings.HasPrefix(k, prefix) {
-			delete(m, k)
-		}
+	if p.scopeMarks != nil {
+		p.scopeMarks[pk] = nil
 	}
 }
 
@@ -708,7 +733,7 @@ func (p *parser) parseAtom() (any, error) {
 		return nil, p.errf("expected a value")
 	}
 	if hasHighByte(tok) && !utf8.ValidString(tok) {
-		return nil, p.errf("invalid UTF-8 in value at byte offset %d", p.pos)
+		return nil, p.errf("invalid UTF-8 in value at byte offset %d", start+invalidUTF8Offset(tok))
 	}
 	// A date may be followed by a space and a time, forming one date-time.
 	if isDateToken(tok) && !p.eof() && p.peek() == ' ' {
@@ -719,7 +744,11 @@ func (p *parser) parseAtom() (any, error) {
 			tok = tok + " " + string(p.src[timeStart:p.pos])
 		}
 	}
-	if v, ok := parseDateTime(tok); ok {
+	v, isDT, dterr := parseDateTime(tok)
+	if dterr != nil {
+		return nil, p.errf("%s", dterr)
+	}
+	if isDT {
 		return v, nil
 	}
 	v, err := decodeNumber(tok)
@@ -758,6 +787,20 @@ func hasHighByte(s string) bool {
 	return false
 }
 
+// invalidUTF8Offset returns the offset of the first byte in s that does not
+// decode as UTF-8, or -1 when all of it does, so an error can name the byte
+// that is invalid rather than the end of the token around it.
+func invalidUTF8Offset(s string) int {
+	for i := 0; i < len(s); {
+		r, size := utf8.DecodeRuneInString(s[i:])
+		if r == utf8.RuneError && size == 1 {
+			return i
+		}
+		i += size
+	}
+	return -1
+}
+
 // --- strings ---------------------------------------------------------------
 
 func (p *parser) parseBasicString() (string, error) {
@@ -895,8 +938,13 @@ func (p *parser) writeContentRune(b *strings.Builder) error {
 
 func (p *parser) parseMultilineString(quote byte, escapes bool) (string, error) {
 	p.skipN(3) // opening delimiter
-	// A newline immediately after the opening delimiter is trimmed.
+	// A newline immediately after the opening delimiter is trimmed, and it is
+	// a newline: a bare CR here is the bare-CR error like anywhere else, not
+	// a newline to trim.
 	if !p.eof() && p.peek() == '\r' {
+		if next, ok := p.peekAt(1); !ok || next != '\n' {
+			return "", p.errf("bare carriage return is not allowed in a string")
+		}
 		p.pos++
 	}
 	if !p.eof() && p.peek() == '\n' {
@@ -1047,7 +1095,10 @@ func (p *parser) readUnicode(n int) (rune, error) {
 	}
 	hex := string(p.src[p.pos : p.pos+n])
 	p.pos += n
-	v, err := strconv.ParseInt(hex, 16, 64)
+	// ParseUint rather than ParseInt: a sign is not a hex digit, and a signed
+	// read would let "\U-0000001" through the range checks below only to
+	// write U+FFFD for a document the grammar rejects.
+	v, err := strconv.ParseUint(hex, 16, 32)
 	if err != nil {
 		return 0, p.errf("invalid unicode escape \\%s", hex)
 	}