In addition to the variants to EXTENDED_SOURCE listed above, EXTENDED_SOURCE_WITH_SEPARATE_SKY exists for very extended sources where it is not possible to nod along the slit, thus a separate sky is used for sky-subtraction. The separate sky is reduced using the REDUCE_SKY calibration recipe.
The following variants are available: EXTENDED_SOURCE_WITH_SEPARATE_SKY_NOFLAT (no division by a flat-field), EXTENDED_SOURCE_WITH_SEPARATE_SKY_NOFLAT_NOSTD (no division by a flat-field or by a standard star), and EXTENDED_SOURCE_WITH_SEPARATE_SKY_NOSTD (no division by a standard star).
ORAC-DR -- spectroscopy data reduction