You sometimes need to specify a reference to a note relative to something else, like the current note. Item Objects are a set of generic relative references to, or placeholders for, another single [sic] note whose actual identity is context sensitive. Item designators are written with lower case starting letters and inter-capitalised if multiword; e.g. child, prevSibling. Usage is case sensitive.
The 'order' of notes, where referred to, relates to their sequence within the overall Tinderbox file. To see this order, expand all levels of an Outline, Explorer or Chart view. The order is the top-to-bottom ordering of the notes on a line by line basis; so the first child's children are ordered before the second child, etc. (Outline order is also exposed via the read-only System attribute $OutlineOrder).