public Set<String> getVariableKeys() {
Set<String> variableKeys = new HashSet<String>();
VariableScopeIterator iter = new VariableScopeIterator(this);
while (iter.hasNext()) {
VariableScope variableScope = iter.next();
Set<String> keys = variableScope.keys();
if (keys!=null) {
variableKeys.addAll(keys);
}
}
return variableKeys;