one=source1
two=source2
three=source3
four=4

two_+_four=%(two)s + %(four)s

[X]
x.one=conf1-sourcex1
x.two=conf1-sourcex2
x.three=conf1-sourcex3

[Y]
y.one=conf1-sourcey1
y.two=conf1-sourcey2
y.three=conf1-sourcey3