public static AttributeMapLookupValue fromKeySourceAttribute(String prefix, String keySourceAttribute, String suffix) {
        return new AttributeMapLookupValue(prefix + "{attribute(" + keySourceAttribute + ")}" + suffix,
                prefix, suffix, "", keySourceAttribute);
    }
This class represents a lookup in a map attribute in a {@link GroupingExpression}.

It evaluates to the value found using the given key for the lookup in that attribute.
The key is either specified explicitly or found via a key source attribute.
Two underlying attributes are used to represent the map attribute (the key and value attributes).

@author geirst
container-search/src/main/java/com/yahoo/search/grouping/request/AttributeMapLookupValue.java