Thank you for explaining how to add the #proxy tag! Sebi, thank you again for implementing this functionality as it provides the first half of what I was hoping for. Since I personally use proxies mostly because I prefer the art to that of the original card, it would be awesome to be able to actually add proxies to inventory. While I certainly don't expect you to add another version of every card in the database to allow for a proxy "set", it would be handy to be able to deselect a set entirely for a card in inventory/decks, and flag it "proxy" with the foil/signed/artist proof/etc dropdown to achieve the same functionality of setting the price to zero in inventory.
If that were implemented, those cards could simply be added to a deck directly as proxies, and pictures of their art could be uploaded to allow the mouse-over functionality when browsing the deck here on Deckbox.
Thank you again, Sebi, for entertaining my wishes for site improvements, and for all that you do!