For each option we state its name (the string supplied by the user to identify the option being set), the values the option may take (Boolean, including ``y'' and ``n''; Integer), a brief description, and the default value when no user-supplied setting is available. Options appear in alphabetical order.
usedmm
y.
ndid
node field
of the node identifier (remaining fields in node identifiers are
always zero).
0.
NOTE: Add remaining option descriptions.