fbool(variable) or fbool(datafield) 

Boolean value will be formatted in according with properties TrueValue and FalseValue. 

Example: 

Property TrueValue set to "Yes" 

var1 is True 

in a report template: 

\var1\ 

formatted var1: \fbool(var1)\ 

in the result: 

True 

formatted var1: Yes