wp_is_valid_utf8( string $bytes ): bool

Note that it’s unlikely for non-UTF-8 data to validate as UTF-8, but it is still possible. Many texts are simultaneously valid UTF-8, valid US-ASCII, and valid ISO-8859-1 (latin1). Example: true === wp_is_valid_utf8( '' ); true === wp_is_valid_utf8( 'just a test' ); true === wp_is_valid_utf8( "\xE2\x9C\x8F" ); // Pencil, U+270F. true === wp_is_valid_utf8( "\u{270F}" ); // Pencil, U+270F. true === wp_is_valid_utf8( '✏' ); // Pencil, U+270F. false === wp_is_valid_utf8( "just xC0 test" ); // Invalid bytes. false === wp_is_valid_utf8( "\xE2\x9C" ); // Invalid/incomplete sequences. false === wp_is_valid_utf8( "\xC1\xBF" ); // Overlong sequences. false === wp_is_valid_utf8( "\xED\xB0\x80" ); // Surrogate halves. false === wp_is_valid_utf8( "B\xFCch" ); // ISO-8859-1 high-bytes. // E.g. The “ü” in ISO-8859-1 is a single byte 0xFC, // but in UTF-8 is the two-byte sequence 0xC3 0xBC. A “valid” string consists of “well-formed UTF-8 code unit sequence[s],” meaning that the bytes conform to the UTF-8 encoding scheme, all characters use the minimal byte sequence required by UTF-8, and that no sequence encodes a UTF-16 surrogate code point or any character above the representable range.