<p>In case-insignificant matches when HasEitherUnicodeFlag(_rer_) is *true*, all characters are implicitly case-folded using the simple mapping provided by the Unicode Standard immediately before they are compared. The simple mapping always maps to a single code point, so it does not map, for example, `ß` (U+00DF LATIN SMALL LETTER SHARP S) to `ss` or `SS`. It may however map code points outside the Basic Latin block to code points within it—for example, `ſ` (U+017F LATIN SMALL LETTER LONG S) case-folds to `s` (U+0073 LATIN SMALL LETTER S) and `K` (U+212A KELVIN SIGN) case-folds to `k` (U+006B LATIN SMALL LETTER K). Strings containing those code points are matched by regular expressions such as `/[a-z]/ui`.</p>
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