It was just a naming proposal, instead of:

GPIO_DS_0_HIGH
GPIO_DS_0_DISCONNECT
and
GPIO_DS_1_HIGH
GPIO_DS_1_DISCONNECT

we would have:
GPIO_DS_DFLT_HIGH (or *_DEFAULT_*)
GPIO_DS_DFLT_DISCONNECT

and:
GPIO_DS_ALT_HIGH (or *_ALTERNATE_*)
GPIO_DS_ALT_DISCONNECT

Of course my naming proposal is bogus. If I understand, should it be
GPIO_DS_OUTPUT_<LOW/HIGH or 0/1>_<HIGH/DISCONNECT> or?

It's just the _0_ and _1_ alone that are not telling anything by themselves.