For example this config file:
a0 = "Goofy"
a1 = "$a0"
a2."$a0" = "Mickey Mouse and " + "$a0"
group1 {
a0 = "Donald Duck"
}
group2 {
a0 = "$a0"
a1 = "$group1.a0"
}
a3 = "$group1.a0"

produces the following:

a0=Goofy
a1=Goofy
a2.Goofy=Mickey Mouse and Goofy
group1.a0=Donald Duck
group2.a0=[:]
group2.a1=[:]
a3=Donald Duck

Applying this patch to ConfigSlurper

— C:/export/java/Groovy/groovy-1.1-beta-3/src/main/groovy/util/ConfigSlurper-save.groovy Fri Sep 21 00:40:58 2007
+++ C:/export/java/Groovy/groovy-1.1-beta-3/src/main/groovy/util/ConfigSlurper.groovy Thu Oct 11 10:10:30 2007
@@ -159,8 +159,9 @@

if(current[name]) { result = current[name] - }

• else { + } else if (config[name]) { + result = config[name] + } else { result = new ConfigObject() current[name] = result }

makes it correctly resolving "group2" references:
group2.a0=Goofy
group2.a1=Donald Duck