In the place list (separated by commas) entries generated by concatenating ofr_tourop and obj_code, example:
<conditions> <obj_tourOpAndCode>TUIP_NBE11060,ADR_APPMED,NPL_60086F</obj_tourOpAndCode> (...)
There is also the possibility of grouping offers into one field, but you must type in your query groups and insert its name in the field group_by,example:
<request> <type>groups</type> <conditions> <group_by>obj_tourOpAndCode</group_by> (...)
List of all code objects (including unavailable ones) is available at http://www.merlinx.pl/mdsws/objlist.csv