package regexp

Import Path
	regexp (on go.dev)

Dependency Relation
	imports 9 packages, and imported by 9 packages

Involved Source Files

	    backtrack.go
	    exec.go
	    onepass.go
	  d regexp.go
		Package regexp implements regular expression search.
		
		The syntax of the regular expressions accepted is the same
		general syntax used by Perl, Python, and other languages.
		More precisely, it is the syntax accepted by RE2 and described at
		https://golang.org/s/re2syntax, except for \C.
		For an overview of the syntax, see the [regexp/syntax] package.
		
		The regexp implementation provided by this package is
		guaranteed to run in time linear in the size of the input.
		(This is a property not guaranteed by most open source
		implementations of regular expressions.) For more information
		about this property, see
		
			https://swtch.com/~rsc/regexp/regexp1.html
		
		or any book about automata theory.
		
		All characters are UTF-8-encoded code points.
		Following [utf8.DecodeRune], each byte of an invalid UTF-8 sequence
		is treated as if it encoded utf8.RuneError (U+FFFD).
		
		There are 16 methods of [Regexp] that match a regular expression and identify
		the matched text. Their names are matched by this regular expression:
		
			Find(All)?(String)?(Submatch)?(Index)?
		
		If 'All' is present, the routine matches successive non-overlapping
		matches of the entire expression. Empty matches abutting a preceding
		match are ignored. The return value is a slice containing the successive
		return values of the corresponding non-'All' routine. These routines take
		an extra integer argument, n. If n >= 0, the function returns at most n
		matches/submatches; otherwise, it returns all of them.
		
		If 'String' is present, the argument is a string; otherwise it is a slice
		of bytes; return values are adjusted as appropriate.
		
		If 'Submatch' is present, the return value is a slice identifying the
		successive submatches of the expression. Submatches are matches of
		parenthesized subexpressions (also known as capturing groups) within the
		regular expression, numbered from left to right in order of opening
		parenthesis. Submatch 0 is the match of the entire expression, submatch 1 is
		the match of the first parenthesized subexpression, and so on.
		
		If 'Index' is present, matches and submatches are identified by byte index
		pairs within the input string: result[2*n:2*n+2] identifies the indexes of
		the nth submatch. The pair for n==0 identifies the match of the entire
		expression. If 'Index' is not present, the match is identified by the text
		of the match/submatch. If an index is negative or text is nil, it means that
		subexpression did not match any string in the input. For 'String' versions
		an empty string means either no match or an empty match.
		
		There is also a subset of the methods that can be applied to text read
		from a RuneReader:
		
			MatchReader, FindReaderIndex, FindReaderSubmatchIndex
		
		This set may grow. Note that regular expression matches may need to
		examine text beyond the text returned by a match, so the methods that
		match text from a RuneReader may read arbitrarily far into the input
		before returning.
		
		(There are a few other methods that do not match this pattern.)
Code Examples

	
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			// Compile the expression once, usually at init time.
			// Use raw strings to avoid having to quote the backslashes.
			var validID = regexp.MustCompile(`^[a-z]+\[[0-9]+\]$`)
		
			fmt.Println(validID.MatchString("adam[23]"))
			fmt.Println(validID.MatchString("eve[7]"))
			fmt.Println(validID.MatchString("Job[48]"))
			fmt.Println(validID.MatchString("snakey"))
		}

	Match
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			matched, err := regexp.Match(`foo.*`, []byte(`seafood`))
			fmt.Println(matched, err)
			matched, err = regexp.Match(`bar.*`, []byte(`seafood`))
			fmt.Println(matched, err)
			matched, err = regexp.Match(`a(b`, []byte(`seafood`))
			fmt.Println(matched, err)
		
		}

	MatchString
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			matched, err := regexp.MatchString(`foo.*`, "seafood")
			fmt.Println(matched, err)
			matched, err = regexp.MatchString(`bar.*`, "seafood")
			fmt.Println(matched, err)
			matched, err = regexp.MatchString(`a(b`, "seafood")
			fmt.Println(matched, err)
		}

	QuoteMeta
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			fmt.Println(regexp.QuoteMeta(`Escaping symbols like: .+*?()|[]{}^$`))
		}

	Regexp_Expand
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			content := []byte(`
			# comment line
			option1: value1
			option2: value2
		
			# another comment line
			option3: value3
		`)
		
			// Regex pattern captures "key: value" pair from the content.
			pattern := regexp.MustCompile(`(?m)(?P<key>\w+):\s+(?P<value>\w+)$`)
		
			// Template to convert "key: value" to "key=value" by
			// referencing the values captured by the regex pattern.
			template := []byte("$key=$value\n")
		
			result := []byte{}
		
			// For each match of the regex in the content.
			for _, submatches := range pattern.FindAllSubmatchIndex(content, -1) {
				// Apply the captured submatches to the template and append the output
				// to the result.
				result = pattern.Expand(result, template, content, submatches)
			}
			fmt.Println(string(result))
		}

	Regexp_ExpandString
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			content := `
			# comment line
			option1: value1
			option2: value2
		
			# another comment line
			option3: value3
		`
		
			// Regex pattern captures "key: value" pair from the content.
			pattern := regexp.MustCompile(`(?m)(?P<key>\w+):\s+(?P<value>\w+)$`)
		
			// Template to convert "key: value" to "key=value" by
			// referencing the values captured by the regex pattern.
			template := "$key=$value\n"
		
			result := []byte{}
		
			// For each match of the regex in the content.
			for _, submatches := range pattern.FindAllStringSubmatchIndex(content, -1) {
				// Apply the captured submatches to the template and append the output
				// to the result.
				result = pattern.ExpandString(result, template, content, submatches)
			}
			fmt.Println(string(result))
		}

	Regexp_Find
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`foo.?`)
			fmt.Printf("%q\n", re.Find([]byte(`seafood fool`)))
		
		}

	Regexp_FindAll
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`foo.?`)
			fmt.Printf("%q\n", re.FindAll([]byte(`seafood fool`), -1))
		
		}

	Regexp_FindAllIndex
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			content := []byte("London")
			re := regexp.MustCompile(`o.`)
			fmt.Println(re.FindAllIndex(content, 1))
			fmt.Println(re.FindAllIndex(content, -1))
		}

	Regexp_FindAllString
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a.`)
			fmt.Println(re.FindAllString("paranormal", -1))
			fmt.Println(re.FindAllString("paranormal", 2))
			fmt.Println(re.FindAllString("graal", -1))
			fmt.Println(re.FindAllString("none", -1))
		}

	Regexp_FindAllStringSubmatch
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a(x*)b`)
			fmt.Printf("%q\n", re.FindAllStringSubmatch("-ab-", -1))
			fmt.Printf("%q\n", re.FindAllStringSubmatch("-axxb-", -1))
			fmt.Printf("%q\n", re.FindAllStringSubmatch("-ab-axb-", -1))
			fmt.Printf("%q\n", re.FindAllStringSubmatch("-axxb-ab-", -1))
		}

	Regexp_FindAllStringSubmatchIndex
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a(x*)b`)
			// Indices:
			//    01234567   012345678
			//    -ab-axb-   -axxb-ab-
			fmt.Println(re.FindAllStringSubmatchIndex("-ab-", -1))
			fmt.Println(re.FindAllStringSubmatchIndex("-axxb-", -1))
			fmt.Println(re.FindAllStringSubmatchIndex("-ab-axb-", -1))
			fmt.Println(re.FindAllStringSubmatchIndex("-axxb-ab-", -1))
			fmt.Println(re.FindAllStringSubmatchIndex("-foo-", -1))
		}

	Regexp_FindAllSubmatch
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`foo(.?)`)
			fmt.Printf("%q\n", re.FindAllSubmatch([]byte(`seafood fool`), -1))
		
		}

	Regexp_FindAllSubmatchIndex
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			content := []byte(`
			# comment line
			option1: value1
			option2: value2
		`)
			// Regex pattern captures "key: value" pair from the content.
			pattern := regexp.MustCompile(`(?m)(?P<key>\w+):\s+(?P<value>\w+)$`)
			allIndexes := pattern.FindAllSubmatchIndex(content, -1)
			for _, loc := range allIndexes {
				fmt.Println(loc)
				fmt.Println(string(content[loc[0]:loc[1]]))
				fmt.Println(string(content[loc[2]:loc[3]]))
				fmt.Println(string(content[loc[4]:loc[5]]))
			}
		}

	Regexp_FindIndex
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			content := []byte(`
			# comment line
			option1: value1
			option2: value2
		`)
			// Regex pattern captures "key: value" pair from the content.
			pattern := regexp.MustCompile(`(?m)(?P<key>\w+):\s+(?P<value>\w+)$`)
		
			loc := pattern.FindIndex(content)
			fmt.Println(loc)
			fmt.Println(string(content[loc[0]:loc[1]]))
		}

	Regexp_FindString
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`foo.?`)
			fmt.Printf("%q\n", re.FindString("seafood fool"))
			fmt.Printf("%q\n", re.FindString("meat"))
		}

	Regexp_FindStringIndex
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`ab?`)
			fmt.Println(re.FindStringIndex("tablett"))
			fmt.Println(re.FindStringIndex("foo") == nil)
		}

	Regexp_FindStringSubmatch
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a(x*)b(y|z)c`)
			fmt.Printf("%q\n", re.FindStringSubmatch("-axxxbyc-"))
			fmt.Printf("%q\n", re.FindStringSubmatch("-abzc-"))
		}

	Regexp_FindSubmatch
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`foo(.?)`)
			fmt.Printf("%q\n", re.FindSubmatch([]byte(`seafood fool`)))
		
		}

	Regexp_FindSubmatchIndex
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a(x*)b`)
			// Indices:
			//    01234567   012345678
			//    -ab-axb-   -axxb-ab-
			fmt.Println(re.FindSubmatchIndex([]byte("-ab-")))
			fmt.Println(re.FindSubmatchIndex([]byte("-axxb-")))
			fmt.Println(re.FindSubmatchIndex([]byte("-ab-axb-")))
			fmt.Println(re.FindSubmatchIndex([]byte("-axxb-ab-")))
			fmt.Println(re.FindSubmatchIndex([]byte("-foo-")))
		}

	Regexp_Longest
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a(|b)`)
			fmt.Println(re.FindString("ab"))
			re.Longest()
			fmt.Println(re.FindString("ab"))
		}

	Regexp_Match
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`foo.?`)
			fmt.Println(re.Match([]byte(`seafood fool`)))
			fmt.Println(re.Match([]byte(`something else`)))
		
		}

	Regexp_MatchString
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`(gopher){2}`)
			fmt.Println(re.MatchString("gopher"))
			fmt.Println(re.MatchString("gophergopher"))
			fmt.Println(re.MatchString("gophergophergopher"))
		}

	Regexp_NumSubexp
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re0 := regexp.MustCompile(`a.`)
			fmt.Printf("%d\n", re0.NumSubexp())
		
			re := regexp.MustCompile(`(.*)((a)b)(.*)a`)
			fmt.Println(re.NumSubexp())
		}

	Regexp_ReplaceAll
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a(x*)b`)
			fmt.Printf("%s\n", re.ReplaceAll([]byte("-ab-axxb-"), []byte("T")))
			fmt.Printf("%s\n", re.ReplaceAll([]byte("-ab-axxb-"), []byte("$1")))
			fmt.Printf("%s\n", re.ReplaceAll([]byte("-ab-axxb-"), []byte("$1W")))
			fmt.Printf("%s\n", re.ReplaceAll([]byte("-ab-axxb-"), []byte("${1}W")))
		
			re2 := regexp.MustCompile(`a(?P<1W>x*)b`)
			fmt.Printf("%s\n", re2.ReplaceAll([]byte("-ab-axxb-"), []byte("$1W")))
			fmt.Printf("%s\n", re2.ReplaceAll([]byte("-ab-axxb-"), []byte("${1}W")))
		
		}

	Regexp_ReplaceAllLiteralString
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a(x*)b`)
			fmt.Println(re.ReplaceAllLiteralString("-ab-axxb-", "T"))
			fmt.Println(re.ReplaceAllLiteralString("-ab-axxb-", "$1"))
			fmt.Println(re.ReplaceAllLiteralString("-ab-axxb-", "${1}"))
		}

	Regexp_ReplaceAllString
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`a(x*)b`)
			fmt.Println(re.ReplaceAllString("-ab-axxb-", "T"))
			fmt.Println(re.ReplaceAllString("-ab-axxb-", "$1"))
			fmt.Println(re.ReplaceAllString("-ab-axxb-", "$1W"))
			fmt.Println(re.ReplaceAllString("-ab-axxb-", "${1}W"))
		
			re2 := regexp.MustCompile(`a(?P<1W>x*)b`)
			fmt.Printf("%s\n", re2.ReplaceAllString("-ab-axxb-", "$1W"))
			fmt.Println(re.ReplaceAllString("-ab-axxb-", "${1}W"))
		
		}

	Regexp_ReplaceAllStringFunc
		package main
		
		import (
			"fmt"
			"regexp"
			"strings"
		)
		
		func main() {
			re := regexp.MustCompile(`[^aeiou]`)
			fmt.Println(re.ReplaceAllStringFunc("seafood fool", strings.ToUpper))
		}

	Regexp_Split
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			a := regexp.MustCompile(`a`)
			fmt.Println(a.Split("banana", -1))
			fmt.Println(a.Split("banana", 0))
			fmt.Println(a.Split("banana", 1))
			fmt.Println(a.Split("banana", 2))
			zp := regexp.MustCompile(`z+`)
			fmt.Println(zp.Split("pizza", -1))
			fmt.Println(zp.Split("pizza", 0))
			fmt.Println(zp.Split("pizza", 1))
			fmt.Println(zp.Split("pizza", 2))
		}

	Regexp_SubexpIndex
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`(?P<first>[a-zA-Z]+) (?P<last>[a-zA-Z]+)`)
			fmt.Println(re.MatchString("Alan Turing"))
			matches := re.FindStringSubmatch("Alan Turing")
			lastIndex := re.SubexpIndex("last")
			fmt.Printf("last => %d\n", lastIndex)
			fmt.Println(matches[lastIndex])
		}

	Regexp_SubexpNames
		package main
		
		import (
			"fmt"
			"regexp"
		)
		
		func main() {
			re := regexp.MustCompile(`(?P<first>[a-zA-Z]+) (?P<last>[a-zA-Z]+)`)
			fmt.Println(re.MatchString("Alan Turing"))
			fmt.Printf("%q\n", re.SubexpNames())
			reversed := fmt.Sprintf("${%s} ${%s}", re.SubexpNames()[2], re.SubexpNames()[1])
			fmt.Println(reversed)
			fmt.Println(re.ReplaceAllString("Alan Turing", reversed))
		}


Package-Level Type Names (only one)

	/* sort by: alphabet | popularity */
	 type Regexp (struct)
		Regexp is the representation of a compiled regular expression.
		A Regexp is safe for concurrent use by multiple goroutines,
		except for configuration methods, such as [Regexp.Longest].

		Methods (total 39)
			(*Regexp) Copy() *Regexp
				Copy returns a new [Regexp] object copied from re.
				Calling [Regexp.Longest] on one copy does not affect another.
				
				Deprecated: In earlier releases, when using a [Regexp] in multiple goroutines,
				giving each goroutine its own copy helped to avoid lock contention.
				As of Go 1.12, using Copy is no longer necessary to avoid lock contention.
				Copy may still be appropriate if the reason for its use is to make
				two copies with different [Regexp.Longest] settings.

			(*Regexp) Expand(dst []byte, template []byte, src []byte, match []int) []byte
				Expand appends template to dst and returns the result; during the
				append, Expand replaces variables in the template with corresponding
				matches drawn from src. The match slice should have been returned by
				[Regexp.FindSubmatchIndex].
				
				In the template, a variable is denoted by a substring of the form
				$name or ${name}, where name is a non-empty sequence of letters,
				digits, and underscores. A purely numeric name like $1 refers to
				the submatch with the corresponding index; other names refer to
				capturing parentheses named with the (?P<name>...) syntax. A
				reference to an out of range or unmatched index or a name that is not
				present in the regular expression is replaced with an empty slice.
				
				In the $name form, name is taken to be as long as possible: $1x is
				equivalent to ${1x}, not ${1}x, and, $10 is equivalent to ${10}, not ${1}0.
				
				To insert a literal $ in the output, use $$ in the template.

			(*Regexp) ExpandString(dst []byte, template string, src string, match []int) []byte
				ExpandString is like [Regexp.Expand] but the template and source are strings.
				It appends to and returns a byte slice in order to give the calling
				code control over allocation.

			(*Regexp) Find(b []byte) []byte
				Find returns a slice holding the text of the leftmost match in b of the regular expression.
				A return value of nil indicates no match.

			(*Regexp) FindAll(b []byte, n int) [][]byte
				FindAll is the 'All' version of [Regexp.Find]; it returns a slice of all successive
				matches of the expression, as defined by the 'All' description in the
				package comment.
				A return value of nil indicates no match.

			(*Regexp) FindAllIndex(b []byte, n int) [][]int
				FindAllIndex is the 'All' version of [Regexp.FindIndex]; it returns a slice of all
				successive matches of the expression, as defined by the 'All' description
				in the package comment.
				A return value of nil indicates no match.

			(*Regexp) FindAllString(s string, n int) []string
				FindAllString is the 'All' version of [Regexp.FindString]; it returns a slice of all
				successive matches of the expression, as defined by the 'All' description
				in the package comment.
				A return value of nil indicates no match.

			(*Regexp) FindAllStringIndex(s string, n int) [][]int
				FindAllStringIndex is the 'All' version of [Regexp.FindStringIndex]; it returns a
				slice of all successive matches of the expression, as defined by the 'All'
				description in the package comment.
				A return value of nil indicates no match.

			(*Regexp) FindAllStringSubmatch(s string, n int) [][]string
				FindAllStringSubmatch is the 'All' version of [Regexp.FindStringSubmatch]; it
				returns a slice of all successive matches of the expression, as defined by
				the 'All' description in the package comment.
				A return value of nil indicates no match.

			(*Regexp) FindAllStringSubmatchIndex(s string, n int) [][]int
				FindAllStringSubmatchIndex is the 'All' version of
				[Regexp.FindStringSubmatchIndex]; it returns a slice of all successive matches of
				the expression, as defined by the 'All' description in the package
				comment.
				A return value of nil indicates no match.

			(*Regexp) FindAllSubmatch(b []byte, n int) [][][]byte
				FindAllSubmatch is the 'All' version of [Regexp.FindSubmatch]; it returns a slice
				of all successive matches of the expression, as defined by the 'All'
				description in the package comment.
				A return value of nil indicates no match.

			(*Regexp) FindAllSubmatchIndex(b []byte, n int) [][]int
				FindAllSubmatchIndex is the 'All' version of [Regexp.FindSubmatchIndex]; it returns
				a slice of all successive matches of the expression, as defined by the
				'All' description in the package comment.
				A return value of nil indicates no match.

			(*Regexp) FindIndex(b []byte) (loc []int)
				FindIndex returns a two-element slice of integers defining the location of
				the leftmost match in b of the regular expression. The match itself is at
				b[loc[0]:loc[1]].
				A return value of nil indicates no match.

			(*Regexp) FindReaderIndex(r io.RuneReader) (loc []int)
				FindReaderIndex returns a two-element slice of integers defining the
				location of the leftmost match of the regular expression in text read from
				the [io.RuneReader]. The match text was found in the input stream at
				byte offset loc[0] through loc[1]-1.
				A return value of nil indicates no match.

			(*Regexp) FindReaderSubmatchIndex(r io.RuneReader) []int
				FindReaderSubmatchIndex returns a slice holding the index pairs
				identifying the leftmost match of the regular expression of text read by
				the [io.RuneReader], and the matches, if any, of its subexpressions, as defined
				by the 'Submatch' and 'Index' descriptions in the package comment. A
				return value of nil indicates no match.

			(*Regexp) FindString(s string) string
				FindString returns a string holding the text of the leftmost match in s of the regular
				expression. If there is no match, the return value is an empty string,
				but it will also be empty if the regular expression successfully matches
				an empty string. Use [Regexp.FindStringIndex] or [Regexp.FindStringSubmatch] if it is
				necessary to distinguish these cases.

			(*Regexp) FindStringIndex(s string) (loc []int)
				FindStringIndex returns a two-element slice of integers defining the
				location of the leftmost match in s of the regular expression. The match
				itself is at s[loc[0]:loc[1]].
				A return value of nil indicates no match.

			(*Regexp) FindStringSubmatch(s string) []string
				FindStringSubmatch returns a slice of strings holding the text of the
				leftmost match of the regular expression in s and the matches, if any, of
				its subexpressions, as defined by the 'Submatch' description in the
				package comment.
				A return value of nil indicates no match.

			(*Regexp) FindStringSubmatchIndex(s string) []int
				FindStringSubmatchIndex returns a slice holding the index pairs
				identifying the leftmost match of the regular expression in s and the
				matches, if any, of its subexpressions, as defined by the 'Submatch' and
				'Index' descriptions in the package comment.
				A return value of nil indicates no match.

			(*Regexp) FindSubmatch(b []byte) [][]byte
				FindSubmatch returns a slice of slices holding the text of the leftmost
				match of the regular expression in b and the matches, if any, of its
				subexpressions, as defined by the 'Submatch' descriptions in the package
				comment.
				A return value of nil indicates no match.

			(*Regexp) FindSubmatchIndex(b []byte) []int
				FindSubmatchIndex returns a slice holding the index pairs identifying the
				leftmost match of the regular expression in b and the matches, if any, of
				its subexpressions, as defined by the 'Submatch' and 'Index' descriptions
				in the package comment.
				A return value of nil indicates no match.

			(*Regexp) LiteralPrefix() (prefix string, complete bool)
				LiteralPrefix returns a literal string that must begin any match
				of the regular expression re. It returns the boolean true if the
				literal string comprises the entire regular expression.

			(*Regexp) Longest()
				Longest makes future searches prefer the leftmost-longest match.
				That is, when matching against text, the regexp returns a match that
				begins as early as possible in the input (leftmost), and among those
				it chooses a match that is as long as possible.
				This method modifies the [Regexp] and may not be called concurrently
				with any other methods.

			(*Regexp) MarshalText() ([]byte, error)
				MarshalText implements [encoding.TextMarshaler]. The output
				matches that of calling the [Regexp.String] method.
				
				Note that the output is lossy in some cases: This method does not indicate
				POSIX regular expressions (i.e. those compiled by calling [CompilePOSIX]), or
				those for which the [Regexp.Longest] method has been called.

			(*Regexp) Match(b []byte) bool
				Match reports whether the byte slice b
				contains any match of the regular expression re.

			(*Regexp) MatchReader(r io.RuneReader) bool
				MatchReader reports whether the text returned by the [io.RuneReader]
				contains any match of the regular expression re.

			(*Regexp) MatchString(s string) bool
				MatchString reports whether the string s
				contains any match of the regular expression re.

			(*Regexp) NumSubexp() int
				NumSubexp returns the number of parenthesized subexpressions in this [Regexp].

			(*Regexp) ReplaceAll(src, repl []byte) []byte
				ReplaceAll returns a copy of src, replacing matches of the [Regexp]
				with the replacement text repl.
				Inside repl, $ signs are interpreted as in [Regexp.Expand].

			(*Regexp) ReplaceAllFunc(src []byte, repl func([]byte) []byte) []byte
				ReplaceAllFunc returns a copy of src in which all matches of the
				[Regexp] have been replaced by the return value of function repl applied
				to the matched byte slice. The replacement returned by repl is substituted
				directly, without using [Regexp.Expand].

			(*Regexp) ReplaceAllLiteral(src, repl []byte) []byte
				ReplaceAllLiteral returns a copy of src, replacing matches of the [Regexp]
				with the replacement bytes repl. The replacement repl is substituted directly,
				without using [Regexp.Expand].

			(*Regexp) ReplaceAllLiteralString(src, repl string) string
				ReplaceAllLiteralString returns a copy of src, replacing matches of the [Regexp]
				with the replacement string repl. The replacement repl is substituted directly,
				without using [Regexp.Expand].

			(*Regexp) ReplaceAllString(src, repl string) string
				ReplaceAllString returns a copy of src, replacing matches of the [Regexp]
				with the replacement string repl.
				Inside repl, $ signs are interpreted as in [Regexp.Expand].

			(*Regexp) ReplaceAllStringFunc(src string, repl func(string) string) string
				ReplaceAllStringFunc returns a copy of src in which all matches of the
				[Regexp] have been replaced by the return value of function repl applied
				to the matched substring. The replacement returned by repl is substituted
				directly, without using [Regexp.Expand].

			(*Regexp) Split(s string, n int) []string
				Split slices s into substrings separated by the expression and returns a slice of
				the substrings between those expression matches.
				
				The slice returned by this method consists of all the substrings of s
				not contained in the slice returned by [Regexp.FindAllString]. When called on an expression
				that contains no metacharacters, it is equivalent to [strings.SplitN].
				
				Example:
				
					s := regexp.MustCompile("a*").Split("abaabaccadaaae", 5)
					// s: ["", "b", "b", "c", "cadaaae"]
				
				The count determines the number of substrings to return:
				
					n > 0: at most n substrings; the last substring will be the unsplit remainder.
					n == 0: the result is nil (zero substrings)
					n < 0: all substrings

			(*Regexp) String() string
				String returns the source text used to compile the regular expression.

			(*Regexp) SubexpIndex(name string) int
				SubexpIndex returns the index of the first subexpression with the given name,
				or -1 if there is no subexpression with that name.
				
				Note that multiple subexpressions can be written using the same name, as in
				(?P<bob>a+)(?P<bob>b+), which declares two subexpressions named "bob".
				In this case, SubexpIndex returns the index of the leftmost such subexpression
				in the regular expression.

			(*Regexp) SubexpNames() []string
				SubexpNames returns the names of the parenthesized subexpressions
				in this [Regexp]. The name for the first sub-expression is names[1],
				so that if m is a match slice, the name for m[i] is SubexpNames()[i].
				Since the Regexp as a whole cannot be named, names[0] is always
				the empty string. The slice should not be modified.

			(*Regexp) UnmarshalText(text []byte) error
				UnmarshalText implements [encoding.TextUnmarshaler] by calling
				[Compile] on the encoded value.

		Implements (at least 4)
			*Regexp : encoding.TextMarshaler
			*Regexp : encoding.TextUnmarshaler
			*Regexp : expvar.Var
			*Regexp : fmt.Stringer
		As Outputs Of (at least 5)
			func Compile(expr string) (*Regexp, error)
			func CompilePOSIX(expr string) (*Regexp, error)
			func MustCompile(str string) *Regexp
			func MustCompilePOSIX(str string) *Regexp
			func (*Regexp).Copy() *Regexp
		As Inputs Of (at least 2)
			func index/suffixarray.(*Index).FindAllIndex(r *Regexp, n int) (result [][]int)
			func internal/profile.(*Profile).Prune(dropRx, keepRx *Regexp)


Package-Level Functions (total 8)

	 func Compile(expr string) (*Regexp, error)
		Compile parses a regular expression and returns, if successful,
		a [Regexp] object that can be used to match against text.
		
		When matching against text, the regexp returns a match that
		begins as early as possible in the input (leftmost), and among those
		it chooses the one that a backtracking search would have found first.
		This so-called leftmost-first matching is the same semantics
		that Perl, Python, and other implementations use, although this
		package implements it without the expense of backtracking.
		For POSIX leftmost-longest matching, see [CompilePOSIX].

	 func CompilePOSIX(expr string) (*Regexp, error)
		CompilePOSIX is like [Compile] but restricts the regular expression
		to POSIX ERE (egrep) syntax and changes the match semantics to
		leftmost-longest.
		
		That is, when matching against text, the regexp returns a match that
		begins as early as possible in the input (leftmost), and among those
		it chooses a match that is as long as possible.
		This so-called leftmost-longest matching is the same semantics
		that early regular expression implementations used and that POSIX
		specifies.
		
		However, there can be multiple leftmost-longest matches, with different
		submatch choices, and here this package diverges from POSIX.
		Among the possible leftmost-longest matches, this package chooses
		the one that a backtracking search would have found first, while POSIX
		specifies that the match be chosen to maximize the length of the first
		subexpression, then the second, and so on from left to right.
		The POSIX rule is computationally prohibitive and not even well-defined.
		See https://swtch.com/~rsc/regexp/regexp2.html#posix for details.

	 func Match(pattern string, b []byte) (matched bool, err error)
		Match reports whether the byte slice b
		contains any match of the regular expression pattern.
		More complicated queries need to use [Compile] and the full [Regexp] interface.

	 func MatchReader(pattern string, r io.RuneReader) (matched bool, err error)
		MatchReader reports whether the text returned by the RuneReader
		contains any match of the regular expression pattern.
		More complicated queries need to use [Compile] and the full [Regexp] interface.

	 func MatchString(pattern string, s string) (matched bool, err error)
		MatchString reports whether the string s
		contains any match of the regular expression pattern.
		More complicated queries need to use [Compile] and the full [Regexp] interface.

	 func MustCompile(str string) *Regexp
		MustCompile is like [Compile] but panics if the expression cannot be parsed.
		It simplifies safe initialization of global variables holding compiled regular
		expressions.

	 func MustCompilePOSIX(str string) *Regexp
		MustCompilePOSIX is like [CompilePOSIX] but panics if the expression cannot be parsed.
		It simplifies safe initialization of global variables holding compiled regular
		expressions.

	 func QuoteMeta(s string) string
		QuoteMeta returns a string that escapes all regular expression metacharacters
		inside the argument text; the returned string is a regular expression matching
		the literal text.

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