Errors pertaining to the failure of various cache operations are indicated
by INKCacheError (enumeration). They are as follows:
INK_CACHE_ERROR_NO_DOC - the key does not match a
cached resource
INK_CACHE_ERROR_DOC_BUSY - e.g, another
continuation could be writing to the cache location
INK_CACHE_ERROR_NOT_READY - the cache is not
ready