diff --git a/validate.go b/validate.go
index 37e5370..0cd782a 100644
--- a/validate.go
+++ b/validate.go
@@ -2,10 +2,16 @@ package agents
 
 import (
 	_ "embed"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
+	"hash/maphash"
 	"regexp"
+	"regexp/syntax"
+	"strconv"
+	"strings"
 	"time"
+	"unicode"
 )
 
 //go:embed crawler-user-agents.json
@@ -80,31 +86,454 @@ var Crawlers = func() []Crawler {
 	return crawlers
 }()
 
-var regexps = func() []*regexp.Regexp {
-	regexps := make([]*regexp.Regexp, len(Crawlers))
+// analyzePattern expands a regular expression to the list of matching texts
+// for plain search. The list is complete, i.e. iff a text matches the input
+// pattern, then it contains at least one of the returned texts. If such a list
+// can't be built, then the resulting list contains one element (main literal),
+// it also returns built regexp object to run in this case. The main literal is
+// a text that is contained in any matching text and is used to optimize search
+// (pre-filter with this main literal before running a regexp). In the case such
+// a main literal can't be found or the regexp is invalid, an error is returned.
+func analyzePattern(pattern string) ([]string, *regexp.Regexp, error) {
+	re, err := syntax.Parse(pattern, syntax.Perl)
+	if err != nil {
+		return nil, nil, fmt.Errorf("re %q does not compile: %w", pattern, err)
+	}
+	re = re.Simplify()
+
+	// Try to convert it to the list of literals.
+	const maxLiterals = 100
+	literals, ok := literalizeRegexp(re, maxLiterals)
+	if ok {
+		return literals, nil, nil
+	}
+
+	// Fallback to using a regexp, but we need some string serving as
+	// an indicator of its possible presence.
+	mainLiteral := findLongestCommonLiteral(re)
+	const minLiteralLen = 3
+	if len(mainLiteral) < minLiteralLen {
+		return nil, nil, fmt.Errorf("re %q does not contain sufficiently long literal to serve an indicator. The longest literal is %q", pattern, mainLiteral)
+	}
+
+	return []string{mainLiteral}, regexp.MustCompile(pattern), nil
+}
+
+// literalizeRegexp expands a regexp to the list of matching sub-strings.
+// Iff a text matches the regexp, it contains at least one of the returned
+// texts. Argument maxLiterals regulates the maximum number of patterns to
+// return. In case of an overflow or if it is impossible to build such a list
+// from the regexp, false is returned.
+func literalizeRegexp(re *syntax.Regexp, maxLiterals int) (literals []string, ok bool) {
+	switch re.Op {
+	case syntax.OpNoMatch:
+		return nil, true
+
+	case syntax.OpEmptyMatch:
+		return []string{""}, true
+
+	case syntax.OpLiteral:
+		return unwrapCase(re, []string{string(re.Rune)}, maxLiterals)
+
+	case syntax.OpCharClass:
+		count := 0
+		for i := 0; i < len(re.Rune); i += 2 {
+			first := re.Rune[i]
+			last := re.Rune[i+1]
+			count += int(last - first + 1)
+		}
+
+		if count > maxLiterals {
+			return nil, false
+		}
+
+		patterns := make([]string, 0, count)
+		for i := 0; i < len(re.Rune); i += 2 {
+			first := re.Rune[i]
+			last := re.Rune[i+1]
+			for r := first; r <= last; r++ {
+				patterns = append(patterns, string([]rune{r}))
+			}
+		}
+
+		return unwrapCase(re, patterns, maxLiterals)
+
+	case syntax.OpAnyCharNotNL, syntax.OpAnyChar:
+		// Not supported.
+		return nil, false
+
+	case syntax.OpBeginLine, syntax.OpBeginText:
+		return []string{"^"}, true
+
+	case syntax.OpEndLine, syntax.OpEndText:
+		return []string{"$"}, true
+
+	case syntax.OpWordBoundary, syntax.OpNoWordBoundary:
+		// Not supported.
+		return nil, false
+
+	case syntax.OpCapture:
+		subList, ok := literalizeRegexp(re.Sub[0], maxLiterals)
+		if !ok {
+			return nil, false
+		}
+
+		return unwrapCase(re, subList, maxLiterals)
+
+	case syntax.OpStar, syntax.OpPlus:
+		// Not supported.
+		return nil, false
+
+	case syntax.OpQuest:
+		if re.Flags&syntax.FoldCase != 0 {
+			return nil, false
+		}
+
+		subList, ok := literalizeRegexp(re.Sub[0], maxLiterals)
+		if !ok {
+			return nil, false
+		}
+		subList = append(subList, "")
+
+		return subList, true
+
+	case syntax.OpRepeat:
+		// Not supported.
+		return nil, false
+
+	case syntax.OpConcat:
+		if re.Flags&syntax.FoldCase != 0 {
+			return nil, false
+		}
+
+		matrix := make([][]string, len(re.Sub))
+		for i, sub := range re.Sub {
+			subList, ok := literalizeRegexp(sub, maxLiterals)
+			if !ok {
+				return nil, false
+			}
+			matrix[i] = subList
+		}
+
+		return combinations(matrix, maxLiterals)
+
+	case syntax.OpAlternate:
+		results := []string{}
+		for _, sub := range re.Sub {
+			subList, ok := literalizeRegexp(sub, maxLiterals)
+			if !ok {
+				return nil, false
+			}
+			results = append(results, subList...)
+		}
+
+		if len(results) > maxLiterals {
+			return nil, false
+		}
+
+		return unwrapCase(re, results, maxLiterals)
+
+	default:
+		// Not supported.
+		return nil, false
+	}
+}
+
+// combinations produces all combination of elements of matrix.
+// Each sub-slice of matrix contributes one part of a resulting string.
+// If the number of combinations is larger than maxLiterals, the function
+// returns false.
+func combinations(matrix [][]string, maxLiterals int) ([]string, bool) {
+	if len(matrix) == 1 {
+		if len(matrix[0]) > maxLiterals {
+			return nil, false
+		}
+
+		return matrix[0], true
+	}
+
+	prefixes := matrix[0]
+	suffixes, ok := combinations(matrix[1:], maxLiterals)
+	if !ok {
+		return nil, false
+	}
+
+	size := len(prefixes) * len(suffixes)
+	if size > maxLiterals {
+		return nil, false
+	}
+
+	results := make([]string, 0, size)
+	for _, prefix := range prefixes {
+		for _, suffix := range suffixes {
+			results = append(results, prefix+suffix)
+		}
+	}
+
+	return results, true
+}
+
+// unwrapCase takes the regexp and the list of patterns expanded from it and
+// further expands it for a case-insensitive regexp, if needed. Argument
+// maxLiterals regulates the maximum number of patterns to return. In case of an
+// overflow, false is returned.
+func unwrapCase(re *syntax.Regexp, patterns []string, maxLiterals int) ([]string, bool) {
+	if re.Flags&syntax.FoldCase == 0 {
+		return patterns, true
+	}
+
+	results := []string{}
+	for _, pattern := range patterns {
+		matrix := make([][]string, len(pattern))
+		for i, r := range pattern {
+			upper := unicode.ToUpper(r)
+			lower := unicode.ToLower(r)
+			matrix[i] = []string{
+				string([]rune{upper}),
+				string([]rune{lower}),
+			}
+		}
+
+		patterns, ok := combinations(matrix, maxLiterals)
+		if !ok {
+			return nil, false
+		}
+
+		results = append(results, patterns...)
+		if len(results) > maxLiterals {
+			return nil, false
+		}
+	}
+
+	return results, true
+}
+
+// findLongestCommonLiteral finds the longest common literal in the regexp. It's
+// such a string which is contained in any text matching the regexp. If such a
+// literal can't be found, it returns an empty string.
+func findLongestCommonLiteral(re *syntax.Regexp) string {
+	if re.Flags&syntax.FoldCase != 0 {
+		return ""
+	}
+
+	switch re.Op {
+	case syntax.OpNoMatch, syntax.OpEmptyMatch:
+		return ""
+
+	case syntax.OpLiteral:
+		return string(re.Rune)
+
+	case syntax.OpCharClass, syntax.OpAnyCharNotNL, syntax.OpAnyChar:
+		return ""
+
+	case syntax.OpBeginLine, syntax.OpBeginText:
+		return "^"
+
+	case syntax.OpEndLine, syntax.OpEndText:
+		return "$"
+
+	case syntax.OpWordBoundary, syntax.OpNoWordBoundary:
+		return ""
+
+	case syntax.OpCapture:
+		return findLongestCommonLiteral(re.Sub[0])
+
+	case syntax.OpStar:
+		return ""
+
+	case syntax.OpPlus:
+		return findLongestCommonLiteral(re.Sub[0])
+
+	case syntax.OpQuest:
+		return ""
+
+	case syntax.OpRepeat:
+		if re.Min >= 1 {
+			return findLongestCommonLiteral(re.Sub[0])
+		}
+
+		return ""
+
+	case syntax.OpConcat:
+		longest := ""
+		for _, sub := range re.Sub {
+			str := findLongestCommonLiteral(sub)
+			if len(str) > len(longest) {
+				longest = str
+			}
+		}
+
+		return longest
+
+	case syntax.OpAlternate:
+		return ""
+
+	default:
+		return ""
+	}
+}
+
+type regexpPattern struct {
+	re    *regexp.Regexp
+	index int
+}
+
+type matcher struct {
+	replacer *strings.Replacer
+	regexps  []regexpPattern
+}
+
+var uniqueToken = hex.EncodeToString((&maphash.Hash{}).Sum(nil))
+
+const (
+	uniqueTokenLen = 2 * 8
+	numLen         = 5
+	literalLabel   = '-'
+	regexpLabel    = '*'
+)
+
+var m = func() matcher {
+	if len(uniqueToken) != uniqueTokenLen {
+		panic("len(uniqueToken) != uniqueTokenLen")
+	}
+
+	regexps := []regexpPattern{}
+	oldnew := make([]string, 0, len(Crawlers)*2)
+
+	// Put re-based patterns to the end to prevent AdsBot-Google from
+	// shadowing AdsBot-Google-Mobile.
+	var oldnew2 []string
+
 	for i, crawler := range Crawlers {
-		regexps[i] = regexp.MustCompile(crawler.Pattern)
+		literals, re, err := analyzePattern(crawler.Pattern)
+		if err != nil {
+			panic(err)
+		}
+
+		label := literalLabel
+		num := i
+		if re != nil {
+			label = regexpLabel
+			num = len(regexps)
+			regexps = append(regexps, regexpPattern{
+				re:    re,
+				index: i,
+			})
+		}
+
+		replaceWith := fmt.Sprintf(" %s%c%0*d ", uniqueToken, label, numLen, num)
+
+		for _, literal := range literals {
+			if re != nil {
+				oldnew2 = append(oldnew2, literal, replaceWith)
+			} else {
+				oldnew = append(oldnew, literal, replaceWith)
+			}
+		}
+	}
+	oldnew = append(oldnew, oldnew2...)
+
+	// Allocate another array with regexps of exact size to save memory.
+	regexps2 := make([]regexpPattern, len(regexps))
+	copy(regexps2, regexps)
+
+	r := strings.NewReplacer(oldnew...)
+	r.Replace("") // To cause internal build process.
+
+	return matcher{
+		replacer: r,
+		regexps:  regexps2,
 	}
-	return regexps
 }()
 
 // Returns if User Agent string matches any of crawler patterns.
 func IsCrawler(userAgent string) bool {
-	for _, re := range regexps {
-		if re.MatchString(userAgent) {
+	// This code is mostly copy-paste of MatchingCrawlers,
+	// but with early exit logic, so it works a but faster.
+
+	text := "^" + userAgent + "$"
+	replaced := m.replacer.Replace(text)
+	if replaced == text {
+		return false
+	}
+
+	for {
+		uniquePos := strings.Index(replaced, uniqueToken)
+		if uniquePos == -1 {
+			break
+		}
+
+		start := uniquePos + uniqueTokenLen + 1
+		if start+numLen >= len(replaced) {
+			panic("corrupt replaced: " + replaced)
+		}
+
+		label := replaced[start-1]
+		switch label {
+		case literalLabel:
 			return true
+		case regexpLabel:
+			// Rare case. Run regexp to confirm the match.
+			indexStr := replaced[start : start+numLen]
+			index, err := strconv.Atoi(indexStr)
+			if err != nil {
+				panic("corrupt replaced: " + replaced)
+			}
+			rp := m.regexps[index]
+			if rp.re.MatchString(userAgent) {
+				return true
+			}
+		default:
+			panic("corrupt replaced: " + replaced)
 		}
+
+		replaced = replaced[start+numLen:]
 	}
+
 	return false
 }
 
 // Finds all crawlers matching the User Agent and returns the list of their indices in Crawlers.
 func MatchingCrawlers(userAgent string) []int {
+	text := "^" + userAgent + "$"
+	replaced := m.replacer.Replace(text)
+	if replaced == text {
+		return []int{}
+	}
+
 	indices := []int{}
-	for i, re := range regexps {
-		if re.MatchString(userAgent) {
-			indices = append(indices, i)
+	for {
+		uniquePos := strings.Index(replaced, uniqueToken)
+		if uniquePos == -1 {
+			break
 		}
+
+		start := uniquePos + uniqueTokenLen + 1
+		if start+numLen >= len(replaced) {
+			panic("corrupt replaced: " + replaced)
+		}
+		indexStr := replaced[start : start+numLen]
+		index, err := strconv.Atoi(indexStr)
+		if err != nil {
+			panic("corrupt replaced: " + replaced)
+		}
+
+		label := replaced[start-1]
+		switch label {
+		case literalLabel:
+			indices = append(indices, index)
+		case regexpLabel:
+			// Rare case. Run regexp to confirm the match.
+			rp := m.regexps[index]
+			if rp.re.MatchString(userAgent) {
+				indices = append(indices, rp.index)
+			}
+		default:
+			panic("corrupt replaced: " + replaced)
+		}
+
+		replaced = replaced[start+numLen:]
 	}
+
 	return indices
 }
diff --git a/validate_test.go b/validate_test.go
index 6812ad2..7d70acb 100644
--- a/validate_test.go
+++ b/validate_test.go
@@ -4,9 +4,467 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"reflect"
+	"regexp/syntax"
+	"sort"
+	"strings"
 	"testing"
 )
 
+// TestAnalyzePattern tests analyzePattern function on many cases, including
+// edge cases.
+func TestAnalyzePattern(t *testing.T) {
+	cases := []struct {
+		input            string
+		wantError        string
+		wantPatterns     []string
+		wantRe           bool
+		shouldMatchRe    []string
+		shouldNotMatchRe []string
+	}{
+		{
+			input:        "simple phrase",
+			wantPatterns: []string{"simple phrase"},
+		},
+		{
+			input:        "^begin anchor",
+			wantPatterns: []string{"^begin anchor"},
+		},
+		{
+			input:        "end anchor$",
+			wantPatterns: []string{"end anchor$"},
+		},
+		{
+			input:        "^both anchors$",
+			wantPatterns: []string{"^both anchors$"},
+		},
+		{
+			input:        "(alter|nation)",
+			wantPatterns: []string{"alter", "nation"},
+		},
+		{
+			input:            "too many [aA][lL][tT][eE][rR][nN][aA][tT][iI][oO][nN][sS]",
+			wantPatterns:     []string{"too many "},
+			wantRe:           true,
+			shouldMatchRe:    []string{"too many ALTERNATIONs"},
+			shouldNotMatchRe: []string{"too many combinations "},
+		},
+		{
+			input: "(alter|nation) concatenation (alter|nation)",
+			wantPatterns: []string{
+				"alter concatenation alter",
+				"alter concatenation nation",
+				"nation concatenation alter",
+				"nation concatenation nation",
+			},
+		},
+		{
+			input: "clas[sS] of [c]haract[eiu]rs",
+			wantPatterns: []string{
+				"clasS of characters",
+				"clasS of charactirs",
+				"clasS of characturs",
+				"class of characters",
+				"class of charactirs",
+				"class of characturs",
+			},
+		},
+		{
+			input: "ranges [0-3]x[a-c]",
+			wantPatterns: []string{
+				"ranges 0xa", "ranges 0xb", "ranges 0xc",
+				"ranges 1xa", "ranges 1xb", "ranges 1xc",
+				"ranges 2xa", "ranges 2xb", "ranges 2xc",
+				"ranges 3xa", "ranges 3xb", "ranges 3xc",
+			},
+		},
+		{
+			input:        "Quest?",
+			wantPatterns: []string{"Ques", "Quest"},
+		},
+		{
+			input:        "Q?ue(st)?",
+			wantPatterns: []string{"Que", "Quest", "ue", "uest"},
+		},
+		{
+			input:            "too many combinations [0-9][a-z]",
+			wantPatterns:     []string{"too many combinations "},
+			wantRe:           true,
+			shouldMatchRe:    []string{"too many combinations 0a"},
+			shouldNotMatchRe: []string{"too many combinations "},
+		},
+		{
+			input:            "negation in char class [^x]",
+			wantPatterns:     []string{"negation in char class "},
+			wantRe:           true,
+			shouldMatchRe:    []string{"negation in char class y"},
+			shouldNotMatchRe: []string{"negation in char class x"},
+		},
+		{
+			input:            "any char .",
+			wantPatterns:     []string{"any char "},
+			wantRe:           true,
+			shouldMatchRe:    []string{"any char x"},
+			shouldNotMatchRe: []string{"any char_x"},
+		},
+		{
+			input:            `word \boundary`,
+			wantPatterns:     []string{"oundary"},
+			wantRe:           true,
+			shouldMatchRe:    []string{"word oundary"},
+			shouldNotMatchRe: []string{"word boundary"},
+		},
+		{
+			input:            "asterisk*",
+			wantPatterns:     []string{"asteris"},
+			wantRe:           true,
+			shouldMatchRe:    []string{"asteris", "asterisk", "asteriskk"},
+			shouldNotMatchRe: []string{"asterik"},
+		},
+		{
+			input:            "plus+",
+			wantPatterns:     []string{"plu"},
+			wantRe:           true,
+			shouldMatchRe:    []string{"plus", "pluss"},
+			shouldNotMatchRe: []string{"plu"},
+		},
+		{
+			input:        "repeat{3,5}$",
+			wantPatterns: []string{"repeattt$", "repeatttt$", "repeattttt$"},
+		},
+		{
+			input:            "repeat{1,120}$",
+			wantPatterns:     []string{"repea"},
+			wantRe:           true,
+			shouldMatchRe:    []string{"repeattt", "repeatttt", "repeattttt"},
+			shouldNotMatchRe: []string{"repea5"},
+		},
+		{
+			input:     "broken re[",
+			wantError: "does not compile",
+		},
+		{
+			input:     "n?o? ?l?o?n?g? ?l?i?t?e?r?a?l?",
+			wantError: "does not contain sufficiently long literal",
+		},
+	}
+
+	for _, tc := range cases {
+		tc := tc
+
+		t.Run(tc.input, func(t *testing.T) {
+			gotPatterns, re, err := analyzePattern(tc.input)
+			if tc.wantError != "" {
+				if err == nil {
+					t.Fatalf("expected to get an error, got success")
+				}
+				if !strings.Contains(err.Error(), tc.wantError) {
+					t.Fatalf("the error returned must contain text %q, got %q", tc.wantError, err.Error())
+				}
+
+				return
+			}
+
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+
+			sort.Strings(tc.wantPatterns)
+			sort.Strings(gotPatterns)
+			if !reflect.DeepEqual(tc.wantPatterns, gotPatterns) {
+				t.Fatalf("returned list of patterns (%#v) does not match the expected value (%#v)", gotPatterns, tc.wantPatterns)
+			}
+
+			if !tc.wantRe {
+				if re != nil {
+					t.Fatalf("unexpectedly got a re")
+				}
+
+				return
+			}
+
+			if re == nil {
+				t.Fatalf("expected to get a re, got nil")
+			}
+			for _, text := range tc.shouldMatchRe {
+				if !re.MatchString(text) {
+					t.Fatalf("test %q must match against the re, but it doesn't", text)
+				}
+			}
+			for _, text := range tc.shouldNotMatchRe {
+				if re.MatchString(text) {
+					t.Fatalf("test %q must not match against the re, but it does", text)
+				}
+			}
+		})
+	}
+}
+
+// TestLiteralizeRegexp tests expansion of a regexp to a list of literals.
+func TestLiteralizeRegexp(t *testing.T) {
+	cases := []struct {
+		input        string
+		maxLiterals  int
+		wantOutput   []string
+		wantOverflow bool
+	}{
+		{
+			input:       "simple phrase",
+			maxLiterals: 100,
+			wantOutput:  []string{"simple phrase"},
+		},
+		{
+			input:       "cases [1-2x-z]",
+			maxLiterals: 100,
+			wantOutput:  []string{"cases 1", "cases 2", "cases x", "cases y", "cases z"},
+		},
+		{
+			input:       "[Ii]gnore case",
+			maxLiterals: 100,
+			wantOutput:  []string{"Ignore case", "ignore case"},
+		},
+		{
+			input:        "overflow [1-2x-z]",
+			maxLiterals:  2,
+			wantOverflow: true,
+		},
+	}
+
+	for _, tc := range cases {
+		tc := tc
+
+		t.Run(tc.input, func(t *testing.T) {
+			re, err := syntax.Parse(tc.input, syntax.Perl)
+			if err != nil {
+				t.Fatalf("failed to parse regexp %q: %v", tc.input, err)
+			}
+
+			gotPatterns, ok := literalizeRegexp(re, tc.maxLiterals)
+			if tc.wantOverflow {
+				if ok {
+					t.Fatalf("expected to get an overflow, got success")
+				}
+
+				return
+			}
+
+			if !ok {
+				t.Fatalf("unexpected overflow")
+			}
+
+			sort.Strings(tc.wantOutput)
+			sort.Strings(gotPatterns)
+			if !reflect.DeepEqual(tc.wantOutput, gotPatterns) {
+				t.Fatalf("returned list of patterns (%#v) does not match the expected value (%#v)", gotPatterns, tc.wantOutput)
+			}
+		})
+	}
+}
+
+// TestCombinations tests combinations() function.
+func TestCombinations(t *testing.T) {
+	cases := []struct {
+		name         string
+		input        [][]string
+		maxLiterals  int
+		wantOutput   []string
+		wantOverflow bool
+	}{
+		{
+			name:        "1x1",
+			input:       [][]string{{"A"}, {"B"}},
+			maxLiterals: 100,
+			wantOutput:  []string{"AB"},
+		},
+		{
+			name:        "0x1",
+			input:       [][]string{{}, {"B"}},
+			maxLiterals: 100,
+			wantOutput:  []string{},
+		},
+		{
+			name:        "1x2",
+			input:       [][]string{{"A"}, {"1", "2"}},
+			maxLiterals: 100,
+			wantOutput:  []string{"A1", "A2"},
+		},
+		{
+			name:        "2x2",
+			input:       [][]string{{"A", "B"}, {"1", "2"}},
+			maxLiterals: 100,
+			wantOutput:  []string{"A1", "A2", "B1", "B2"},
+		},
+		{
+			name:        "empty string as an option",
+			input:       [][]string{{"A", ""}, {"1", "2"}},
+			maxLiterals: 100,
+			wantOutput:  []string{"A1", "A2", "1", "2"},
+		},
+		{
+			name:         "overflow",
+			input:        [][]string{{"A", "B"}, {"1", "2"}},
+			maxLiterals:  3,
+			wantOverflow: true,
+		},
+	}
+
+	for _, tc := range cases {
+		tc := tc
+
+		t.Run(tc.name, func(t *testing.T) {
+			gotPatterns, ok := combinations(tc.input, tc.maxLiterals)
+			if tc.wantOverflow {
+				if ok {
+					t.Fatalf("expected to get an overflow, got success")
+				}
+
+				return
+			}
+
+			if !ok {
+				t.Fatalf("unexpected overflow")
+			}
+
+			sort.Strings(tc.wantOutput)
+			sort.Strings(gotPatterns)
+			if !reflect.DeepEqual(tc.wantOutput, gotPatterns) {
+				t.Fatalf("returned list of patterns (%#v) does not match the expected value (%#v)", gotPatterns, tc.wantOutput)
+			}
+		})
+	}
+}
+
+// TestUnwrapCase tests unwrapping literals of case-insensitive regexps.
+func TestUnwrapCase(t *testing.T) {
+	cases := []struct {
+		name          string
+		ignoreCase    bool
+		inputPatterns []string
+		maxLiterals   int
+		wantOutput    []string
+		wantOverflow  bool
+	}{
+		{
+			name:          "simple phrase",
+			inputPatterns: []string{"simple phrase"},
+			maxLiterals:   100,
+			wantOutput:    []string{"simple phrase"},
+		},
+		{
+			name:          "ignore case",
+			ignoreCase:    true,
+			inputPatterns: []string{"i"},
+			maxLiterals:   100,
+			wantOutput:    []string{"i", "I"},
+		},
+		{
+			name:          "ignore case two letters",
+			ignoreCase:    true,
+			inputPatterns: []string{"ic"},
+			maxLiterals:   100,
+			wantOutput:    []string{"IC", "Ic", "iC", "ic"},
+		},
+		{
+			name:          "ignore case two words",
+			ignoreCase:    true,
+			inputPatterns: []string{"i", "c"},
+			maxLiterals:   100,
+			wantOutput:    []string{"C", "I", "c", "i"},
+		},
+		{
+			name:          "ignore case overflow",
+			ignoreCase:    true,
+			inputPatterns: []string{"long text"},
+			maxLiterals:   100,
+			wantOverflow:  true,
+		},
+	}
+
+	for _, tc := range cases {
+		tc := tc
+
+		t.Run(tc.name, func(t *testing.T) {
+			re := &syntax.Regexp{}
+			if tc.ignoreCase {
+				re.Flags = syntax.FoldCase
+			}
+
+			gotPatterns, ok := unwrapCase(re, tc.inputPatterns, tc.maxLiterals)
+			if tc.wantOverflow {
+				if ok {
+					t.Fatalf("expected to get an overflow, got success")
+				}
+
+				return
+			}
+
+			if !ok {
+				t.Fatalf("unexpected overflow")
+			}
+
+			sort.Strings(tc.wantOutput)
+			sort.Strings(gotPatterns)
+			if !reflect.DeepEqual(tc.wantOutput, gotPatterns) {
+				t.Fatalf("returned list of patterns (%#v) does not match the expected value (%#v)", gotPatterns, tc.wantOutput)
+			}
+		})
+	}
+}
+
+// TestFindLongestCommonLiteral tests finding longest literal in a regexp.
+func TestFindLongestCommonLiteral(t *testing.T) {
+	cases := []struct {
+		input      string
+		wantOutput string
+	}{
+		{
+			input:      "simple phrase",
+			wantOutput: "simple phrase",
+		},
+		{
+			input:      "simple (phrase)?",
+			wantOutput: "simple ",
+		},
+		{
+			input:      "[iI]",
+			wantOutput: "",
+		},
+		{
+			input:      "[i]b",
+			wantOutput: "ib",
+		},
+		{
+			input:      "simple (phrase)+",
+			wantOutput: "simple ",
+		},
+		{
+			input:      "a*",
+			wantOutput: "",
+		},
+		{
+			input:      "(abc)|(ab)",
+			wantOutput: "",
+		},
+	}
+
+	for _, tc := range cases {
+		tc := tc
+
+		t.Run(tc.input, func(t *testing.T) {
+			re, err := syntax.Parse(tc.input, syntax.Perl)
+			if err != nil {
+				t.Fatalf("failed to parse regexp %q: %v", tc.input, err)
+			}
+
+			gotOutput := findLongestCommonLiteral(re)
+
+			if gotOutput != tc.wantOutput {
+				t.Fatalf("returned value (%q) does not match the expected value (%q)", gotOutput, tc.wantOutput)
+			}
+		})
+	}
+}
+
 func contains(list []int, value int) bool {
 	for _, elem := range list {
 		if elem == value {