When obtaining an NDF identifier for a data structure using NDF_FIND,
the NDF library has to decide what mode of access to grant
(i.e. whether it should allow the NDF to be modified or whether it
should be ``read only''). It normally does this by inspecting the
locator supplied and permitting
modification of the NDF only if the
locator itself permitted modification of the data structure. Access
can subsequently be further restricted, if required, using NDF_NOACC
(see §).
However, if the locator supplied has the value DAT__ROOT (indicating
that an absolute NDF name has been given), then this method cannot be
applied. In this case, read only access will be obtained by NDF_FIND
and subsequent modification of the NDF will not be permitted. If the
ability to modify the NDF is required, the routine NDF_OPEN should be
used instead, as this allows the access mode to be specified (see
§).