If you're a Workshop modder and you want to make your mod's custom inventory items play nice with the weapon selector, here's what you'll want to do.

In your inventory class, there are two default properties you'll need to set: InventoryGroup and GroupOffset.

InventoryGroup determines which row your item will appear in. Currently, four values are supported:

• 100 Health and Powerup items
  
• 101 Animals, animal control, and fish finder items
  
• 102 Errand-related items
  
• 103 Everything else

If an item's InventoryGroup does not match any of the above values, it will appear in the last row (103 Everything else), though sometimes the item won't appear at all in the selector, so setting a proper value for InventoryGroup is crucial.

GroupOffset determines where in the row your item will appear. Items with a lower GroupOffset will appear to the left of items with a higher GroupOffset. Many of the game's default items already have low GroupOffset items, so I'd recommend starting somewhere around 20 or 30 for this value. If two items share the same InventoryGroup and GroupOffset, the order is determined based on which item the player received first - there should be no conflicts, so don't worry too much about using the same value as another modder, though I recommend keeping your own items in order if possible.