These latter writings, together with a few letters, are the only extant material out of which a biography of him can be framed.

There is very little extant material for his reign.

The text is the oldest extant printed material in the world for several reasons.

Many are listed in the Skáldatal, not all of whom are known from extant material.

There is very little extant written material available from this period, though there is a considerable amount from later periods that may be relevant.

Because virtually all extant written material on Arianism was written by its opponents, the nature of Arian teachings is difficult to define precisely today.

With the approval of the BBC, efforts are now under way to restore as many of the episodes as possible from the extant material.

This still leaves over half the extant material unreleased in any form.

Their attempt to apply Kaufman's and Justeson's decipherments to other extant Isthmian material failed to produce any meaningful results.

To ensure the continuation of their race, Rassilon created the Looms, machines that would "weave" new Gallifreyans out of extant genetic material.