Collection<String> touchedFields() {
            Collection<String> output = touchedFields;
            touchedFields = null; // deny re-use to try and avoid obvious bugs
            return output;
        }
An indexing language script derived from a schema. An indexing script contains a set of indexing
statements, organized in a composite structure of indexing code snippets.

@author bratseth
config-model/src/main/java/com/yahoo/schema/derived/IndexingScript.java