just read the article "Did you know? Linking entries and box sets" which mentions that it's possible to link e.g. box-set DVDs together by drag&drop.
But how is that supposed to work? If I select a DVD I want to link to another, the InfoView immediately switches to that movie and I have no chance to drag it to the InfoView of the desired target?!?
To select multiple entries, hold down the Command key while selecting the entries.
If you only want to link the entries to one entry, make sure that's the last one you select (so it's the one showing in the info view) and then drag your selection of entries over that entry. (Don't worry - the entry selected won't link to itself.)
If you want to link all the selected entries to each other, hold down the Option key while you drag the entries over the info view.
