# Locale for regexp-quote
**URL:** https://racket.discourse.group/t/locale-for-regexp-quote/2988
**Category:** General
**Created:** [July 1, 2024, 5:02am UTC](https://racket.discourse.group/t/locale-for-regexp-quote/2988 "2024-07-01T05:02:37Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@sorawee](https://racket.discourse.group/u/sorawee)
#### Post date: [July 1, 2024, 5:02am UTC](https://racket.discourse.group/t/locale-for-regexp-quote/2988/1 "2024-07-01T05:02:37Z")
@gus-massa asked in [Fix regexps docs by gus-massa · Pull Request #5027 · racket/racket · GitHub](https://github.com/racket/racket/pull/5027)
> Which locale is used in `regexp-quote` when it compare bytes in case insensitive?
```scheme
(regexp-match (regexp-quote #"Á" #f) #"á") ; ==> (#"\341")
(regexp-match (regexp-quote #"á" #f) #"Á") ; ==> (#"\301")
(regexp-match (regexp-quote #"A" #f) #"a") ; ==> (#"a")
(regexp-match (regexp-quote #"a" #f) #"A") ; ==> (#"A")
```
Not sure if this is relevant? [What locale is for string-upcase?](https://racket.discourse.group/t/what-locale-is-for-string-upcase/2203)
---
### Author:  [@shawnw](https://racket.discourse.group/u/shawnw)
#### Post date: [July 1, 2024, 6:30am UTC](https://racket.discourse.group/t/locale-for-regexp-quote/2988/2 "2024-07-01T06:30:19Z")
Telling `regexp-quote` to make a case-insensitive pattern just wraps the escaped pattern in a `(?i:...)`:
```scheme
> (regexp-quote #"Á" #f)
#"(?i:\301)"
```
Did some digging in the source, and _if_ I'm following it correctly (A big if since I didn't spend that much time digging in), when in case-insensitive mode, literal characters/bytes are added to a range of codepoints/bytes that can match with [this function](https://github.com/racket/racket/blob/master/racket/src/regexp/parse/case.rkt):
```scheme
(define (range-add* range c config)
(cond
[(not c) range]
[else
(define range2 (range-add range c))
(cond
[(parse-config-case-sensitive? config) range2]
[else
(define range3 (range-add range2 (char->integer (char-upcase (integer->char c)))))
(define range4 (range-add range3 (char->integer (char-foldcase (integer->char c)))))
(range-add range4 (char->integer (char-downcase (integer->char c))))])]))
```
`c` is for string regular expressions the codepoint, and for byte regexps, the byte in question. So it's effectively using Latin-1 case mappings for byte regexps (Since Latin-1 corresponds to the first 256 codepoints in Unicode).
* * *
Aside: the Reference says of mixing string and bytestring regexps and text:
> If a character regexp is used with a byte string or input port, it matches UTF-8 encodings (see [Encodings and Locales](https://docs.racket-lang.org/reference/encodings.html)) of matching character streams; if a byte regexp is used with a character string, it matches bytes in the UTF-8 encoding of the string.
but the above routine means you can't do case-insensitive matching of non-ASCII characters when using a byte regexp and a string match text:
```scheme
> (regexp-match? (string->bytes/utf-8 "(?i:Á)") "Á")
#t
> (regexp-match? (string->bytes/utf-8 "(?i:Á)") "á") ; fails!
#f
> (regexp-match? (string->bytes/utf-8 "(?i:A)") "A")
#t
> (regexp-match? (string->bytes/utf-8 "(?i:A)") "a")
#t
```
The other way around works though:
```scheme
> (regexp-match? #rx"(?i:Á)" (string->bytes/utf-8 "á"))
#t
```