where is used to restrict attention to a specified set of episodes. For example, given the following case fragment:
01 Jun 03 20 Jun 03 30 Jun 03 15 Oct 03 02 Nov 03 HDL 2.0 2.1 2.2 2.5 1.9 LDL 6.2* 5.0* 3.5 3.9 Trig 3.0 1.9 LipidDrug N Y Y N
at least 1 LDL is high, where Notes is “Y”
no HDL where is high, where LDL is high