Here was my thought process: you added this because below there's an expression, `"@xmlns" in doc`, that raises an error if doc is a schema list (`LazySchemaList`). jsonobject doesn't have a different class for schema lists versus other lists, so this check doesn't work anymore (or would inadvertently filter out normal lists as well!)

Instead, I opted for what I felt was a more explicit check down near `"@xmlns" in doc`. You basically only to ask about `"@xmlns" in doc` if doc is a DocumentSchema (or possibly a dict, wasn't sure about that), so I just check that.