private Document execute(Document input) throws IOException, TransformerException {
        for (PreProcessor preProcessor : chain) {
            input = preProcessor.process(input);
        }
        return input;
    }
A preprocessor for services.xml files that handles deploy:environment, deploy:region, preprocess:properties, preprocess:include
and create a new Document which is based on the supplied environment and region

@author hmusum
config-application-package/src/main/java/com/yahoo/config/application/XmlPreProcessor.java