The AL maintains considerable state. This documents enumerates
each state variable and describes how each variable can be
changed. For purposes of discussion, state variables are
categorized somewhat arbitrarily by their function. For example,
although we describe operations that the AL performs on the
implied output buffer, the outbut buffer is not part of the
AL state. Certain states of AL objects (e.g. buffer states
with respect to queueing) are introduced for discussion purposes,
but not exposed through the API.