Used when referencing Boolean values that are represented with the strings true and false rather than the number 0 and 1. Takes one argument.
This function returns:
0– the argument is logically false. The following are considered true: the string true, a Boolean true, and a non-zero integer. (Anything else is considered false.)
1– the argument is logically true.
The following expression returns 0.
<isTrue> <s>false</s> </isTrue>