我不认为有任何关于这方面的官方文件，但你可以看看sanitize_user 中的函数wp-includes/formatting.php :

function sanitize_user( $username, $strict = false ) {
    $raw_username = $username;
    $username = wp_strip_all_tags( $username );
    $username = remove_accents( $username );
    // Kill octets
    $username = preg_replace( \'|%([a-fA-F0-9][a-fA-F0-9])|\', \'\', $username );
    $username = preg_replace( \'/&.+?;/\', \'\', $username ); // Kill entities

    // If strict, reduce to ASCII for max portability.
    if ( $strict )
        $username = preg_replace( \'|[^a-z0-9 _.\\-@]|i\', \'\', $username );

    $username = trim( $username );
    // Consolidate contiguous whitespace
    $username = preg_replace( \'|\\s+|\', \' \', $username );

    return apply_filters( \'sanitize_user\', $username, $raw_username, $strict );
}