@Override
            protected void doVisit(Expression expression) {
                if (expression instanceof InputExpression in) {
                    inputs.add(in.getFieldName());
                }
                if (expression instanceof OutputExpression out) {
                    outputs.add(out.getFieldName());
                }
            }
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