Only synchronize certain file types

I need to synchronize files, both directions, between local and an FTP server. Thing is I only want .x and .y files taken into account. I.e. both locally and remotely, other files and directories containing only other files, shouldn't be touched.

I'm sure I need to use the Include and Exclude Masks, but find this section a bit confusing:

Both include and exclude part can be empty, denoting that everything is included or nothing is excluded, respectively. When include part is empty, masks starts with pipe straight away.

I'm thinking the following command should do what I want, but what does "nothing is excluded" mean? Does it mean what I think? If nothing is excluded, isn't everything included either way?

Your mask is correct.

The trailing pipe (|) is not necessary.

Thanks :)