-/* Return true if the text immediately before POS in BUF is known, for
- the purposes of CACHE. If NEXT is non-zero, set *NEXT to the nearest
- position before POS where the knownness changes. */
+/* Return the value for the text immediately before POS in BUF if the
+ value is known, for the purposes of CACHE, and return zero
+ otherwise. If NEXT is non-zero, set *NEXT to the nearest
+ position before POS where the knowledge changes. */