A complex example

Consider the following expression as read by a person familiar with mathematical notation:

[displaymath5894]

The experienced reader is able to quickly scan the above expression and, while perusing the denominator, access the numerator. This ability is a consequence of internalizing the underlying structure conveyed by the visual layout and using it to traverse the information. The atomic actions in accessing the numerator are:

1. Mark current node.
2. Read previous sibling.
3. Return to marked node.

We enable audio browsing by allowing a listener to perform the same kind of traversals. AsTeR internalizes a sufficiently rich structure to permit all of these browsing actions.