Function contains

contains(string: string, substring: string, locale?: string): boolean
Checks whether a string contains another, ignoring diacritics and case.

Uses Intl.Collator for accent- and case-insensitive matching. An empty substring always matches.
Parameters
- string: string
  Haystack to search within (normalized to NFC before comparison).
- substring: string
  Needle to find; empty string always matches.
- locale: string = "en"
  Locale for accent- and case-insensitive matching via Intl.Collator. Defaults to "en".
Returns boolean
true when substring appears in string per collator rules; false otherwise.
Example
```
contains("café", "cafe"); // true
contains("Hello World", "world"); // true
contains("hello", ""); // true (empty needle always matches)
contains("hello", "bye"); // false
```
- Defined in string.ts:40