Auto

Default strategy. Prefetch is conservative and adaptive to document size:

• Small documents (≤ LARGE_DOCUMENT_THRESHOLD pages) use a symmetric window (DEFAULT_PAGES_BEFORE before, DEFAULT_PAGES_AFTER after) — scrolling either way stays warm.

• Large documents (>LARGE_DOCUMENT_THRESHOLD pages) tighten to a forward-biased window (LARGE_DOCUMENT_PAGES_BEFORE before, LARGE_DOCUMENT_PAGES_AFTER after). On a 1000-page manual there is no point eagerly rasterising a wide ring around the viewport: the memory budget would evict it before the user reaches it, and the wasted renders compete with the visible page for the render mutex. Biasing the window forward matches the dominant read-downward scroll direction.

Everything beyond the window is left to the memory budget. Recommended for most apps.