I'd seen dimmed properties before, and I always thought of them as the properties that are there by default, or ones I'm not supposed to manipulate. It turns out that's pretty much correct. The technical term for that is that dimmed properties are non-enumerable vs. enumerable properties.
Linked lists are very similar to arrays in that they are a one-dimensional list of elements. Unlike arrays, however, in a linked list, you cannot just jump to index 4, you have to walk through the list, starting with the "head", or the first element in the list, and work your way through to the fourth element. They are very useful for lists where you need to add/remove elements, but not so useful if you need to search elements.