<ModType>City</ModType>
<Attribute>UnlockImprovement</Attribute>
<BoolVal1>1</BoolVal1>
<StrVal>Conclave</StrVal>
In this example consider the BoolVal1 as an if statement so the test here is:
if {City} has unlocked {Conclave} = true then [Prereq = ok]
if BoolVal1 had been =0 then it would have checked for:
if {City} has unlocked {Conclave} = false then [Prereq = ok]
at least that's what my programming experience would tell me