You first need to be in the sub-collection...

1/ Select the item(s) you want to remove from the sub-collection

2/ Right click on the item (context menu) and select 'Remove item(s) from collection'

3/ Select 'OK' to confirm or 'Cancel' to abandon

(Also, everything is always in the main collection ('My Library') - sub-collections are only views of sub-sets of the total data

Ok, it looks like you're selecting an attachment rather than the parent item?

The options in your screenshot only appear when you right-click on a child attachment.

So that's what @ajb59 was saying — if you want to remove an item from the collection, you need to do it from the parent item.

- only

https://www.zotero.org/support/collections_and_tags#removing_items_from_a_collection

No, you're just confused here. All collection operations have to be done to parent items, not child items. Again, your screenshot shows you right-clicking on a child item. You can't drag a child item to a collection either.

I'm really not confused - I understand the situation perfectly. I understand that just because an item is in a sub-collection it is still in its collection.

But I make a sub-collection and add items to it for a function; when the function changes or the item changes I might want to change the sub-collection by editing it.

No, that is incorrect. A subcollection isn't some distinct thing. It's just a collection. You remove an item from any collection the same way — as shown in the documentation I linked to. If an item is in a collection and also in one of its subcollections, and you remove the item from the subcollection, the item still exists in the collection.

If you're going to post here, please trust that we know what we're talking about and are capable of telling you when you're confused. You posted a screenshot of the context menu for a child attachment. That has nothing — nothing whatsoever — to do with your question about removing items from a collection, and the fact that you posted it shows that you're misunderstanding something fundamental here.

You can explain further what you're not understanding, and provide screenshots with more context, but don't tell us what Zotero can and can't do. I promise you we know.

The confusion seems to be stemming from a misunderstanding of the terminology that Zotero uses.

Collection and subcollection refer to the folders in the left-hand panel.
Items are the books, articles etc in the main panel.

A top-level ITEM is called a "parent" item. A file that is attached to an item (such as a PDF or snapshot) is called a "child item" of the parent.

"Parent" does NOT refer to the collection that the sub-collection is in, but to the ITEM that's in the collection.

From the screenshot it seems that dbrear is right-clicking on a file that's attached to an item (that is, clicking on a "child" not the "parent" item).

Right-clicking on the ITEM (rather than the attachment) brings up a context menu with the option to "Remove item from collection".

https://s3.amazonaws.com/zotero.org/images/forums/u405809/fidew8ru1qiqt8n9iz3u.png

Although claude70's suggestion doesn't quite meet the case, I am happy to report that I have created a test sub-collection and added a test item in it (an item with am attached file), and when I right-click on the item in the sub-collection I am offered the opportunity to Remove item from collection ..., as I would have expected, but which wasn't working originally. I just need to remember that a sub-collection is a collection.

So we can all get on with our normal lives. I'd like to thank all who spent so much time on this with me, particularly dstillman.