Using custom HTML tags to WordPress [closed]

You can expand list of KSES allowed tags (and their attributes):

add_filter('wp_kses_allowed_html', 'wpse_283385_blocktip_tag');
function wpse_283385_blocktip_tag($allowed_tags) {
    $allowed_tags['blocktip'] = array(
        'name' => true,
        'id' => true,
        'class' => true,
        'style' => true
    );

    return $allowed_tags;
}

add_filter('tiny_mce_before_init', 'wpse_283385_blocktip_tag_tinymce');
function wpse_283385_blocktip_tag_tinymce($init) {
    $tags="blocktip[*]";

    if ( isset( $init['extended_valid_elements'] ) ) {
        $init['extended_valid_elements'].= ','.$tags;
    } else {
        $init['extended_valid_elements'] = $tags;
    }

    return $init;
}

If you need more attributes for that tag, add them in the array in the first function, or add them to $tags (comma separated) in the second.