Some characters are stripped from documentation

Read the example in src/wp-includes/utf8.php and compare it with the rendered wp_is_valid_utf8() documentation. Trace how the PHP example is parsed, focusing on the missing \x and ✏ characters. Done means the documented example preserves both differences shown in the issue.

For example, wp_is_valid_utf8() includes this example text:

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.

However, the documented example is this:

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.

Differences:

• just \xC0 test becomes just xC0 test
• ✏ is removed