diff --git a/parser.go b/parser.go
index 78a3ac1..e4b39af 100644
--- a/parser.go
+++ b/parser.go
@@ -36,7 +36,7 @@ var hexRE = regexp.MustCompile(`(?i)(\|(?:\s*[a-f0-9]{2}\s*)+\|)`)
 var escapeRE = regexp.MustCompile(`([()+.'\\])`)
 
 // escapeContent matches escaped special characters.
-var escapeContent = regexp.MustCompile(`\\([\\;":])`)
+var escapeContent = regexp.MustCompile(`\\([\\;":|\[\]+ .])`)
 
 // metaSplitRE matches string in metadata.
 var metaSplitRE = regexp.MustCompile(`,\s*`)
@@ -386,7 +386,7 @@ func containsUnescaped(s string) bool {
 	for _, b := range s {
 		if esc {
 			switch b {
-			case '\\', ';', '"', ':':
+			case '\\', ';', '"', ':', '|', '[', ']', '+', '.', ' ':
 				esc = false
 			default:
 				return true
@@ -630,13 +630,22 @@ func (r *Rule) option(key item, l *lexer) error {
 		"dce_iface", "dce_opnum", "dce_stub_data",
 		"asn1"}):
 		nextItem := l.nextItem()
+		negate := false
+		if nextItem.typ == itemNot {
+			negate = true
+			nextItem = l.nextItem()
+		}
 		if nextItem.typ != itemOptionValue {
 			return fmt.Errorf("no valid value for %s tag", key.value)
 		}
 		if r.Tags == nil {
 			r.Tags = make(map[string]string)
 		}
-		r.Tags[key.value] = nextItem.value
+		if negate {
+			r.Tags[key.value] = "!" + nextItem.value
+		} else {
+			r.Tags[key.value] = nextItem.value
+		}
 	case inSlice(key.value, []string{"sameip", "tls.store", "ftpbounce"}):
 		r.Statements = append(r.Statements, key.value)
 	case inSlice(key.value, tlsTags):
diff --git a/parser_test.go b/parser_test.go
index 5fabdb5..0eae640 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -604,6 +604,31 @@ func TestParseRule(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "negated tags",
+			rule: `alert tcp any any -> any any (msg:"test"; fragbits:!M; flags:!F; tos:!0; ipopts:!rr; sid:1; rev:1;)`,
+			want: &Rule{
+				Action:   "alert",
+				Protocol: "tcp",
+				Source: Network{
+					Nets:  []string{"any"},
+					Ports: []string{"any"},
+				},
+				Destination: Network{
+					Nets:  []string{"any"},
+					Ports: []string{"any"},
+				},
+				SID:         1,
+				Revision:    1,
+				Description: "test",
+				Tags: map[string]string{
+					"fragbits": "!M",
+					"flags":    "!F",
+					"tos":      "!0",
+					"ipopts":   "!rr",
+				},
+			},
+		},
 		{
 			name: "commented rule content",
 			rule: `#alert udp $HOME_NET any -> $EXTERNAL_NET any (sid:1337; msg:"foo"; content:"AA"; rev:2;)`,
@@ -2139,6 +2164,25 @@ func TestParseRule(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "content match with escaped pipe and characters",
+			rule: `alert tcp any any -> any any (msg:"test"; content:"\|test\| \[abc\] \+ \. \ "; sid:1; rev:1;)`,
+			want: &Rule{
+				Action:      "alert",
+				Protocol:    "tcp",
+				Source:      Network{Nets: []string{"any"}, Ports: []string{"any"}},
+				Destination: Network{Nets: []string{"any"}, Ports: []string{"any"}},
+				SID:         1,
+				Revision:    1,
+				Description: "test",
+				Matchers: []orderedMatcher{
+					&Content{
+						DataPosition: pktData,
+						Pattern:      []byte("|test| [abc] + .  "),
+					},
+				},
+			},
+		},
 		// Errors
 		{
 			name:    "invalid action",
@@ -2364,6 +2408,21 @@ func TestContainsUnescaped(t *testing.T) {
 			input: `\\\\\\\\\;`,
 			want:  false,
 		},
+		{
+			name:  "escaped pipe",
+			input: `\|`,
+			want:  false,
+		},
+		{
+			name:  "escaped bracket",
+			input: `\[`,
+			want:  false,
+		},
+		{
+			name:  "escaped plus dot space",
+			input: `\+\.\ `,
+			want:  false,
+		},
 	} {
 		got := containsUnescaped(tt.input)
 		if got != tt.want {