Add attributes

Add custom attributes to the item editor where each item can set them to different values

// PowerScrolls example
provider.addAddon(
    new PluginAddon("PowerScrolls", XMaterial.WRITABLE_BOOK.get())
        .attribute(
            new AddonAttribute<>(
                "Is a scroll", // Attribute name
                XMaterial.WRITTEN_BOOK.get(), // GUI material
                false, // Default value
                (player, gui, editor, callback) -> {
                    Boolean current = (Boolean) editor
                        .getAttributeSerializableByName("PowerScrolls_Is a scroll") // Name format is "%AddonName%_%AttributeName%"
                        .getValue();

                    callback.result(!current); // Callback the new value
                    editor.createAddonGui(provider.getAddonByName("PowerScrolls"))
                          .openInventory(player); // Create a new gui for the addon and open it to the player
                },
                "&7If true, the item will be used to upgrade",
                "&7other items and add abilities to them.",
                "",
                "&aClick to toggle" // Some lore to explain what this attribute does.
            )
        )
);