public B withField(String fieldName) {
            failIfAlreadyBuilt();
            wantedFieldNames.add(fieldName);
            return (B)this;
        }
Specify an additional field that we want to retrieve.
@param fieldName The name of the additional field
@return the current Builder instance.
analyzer/src/main/java/nl/basjes/parse/useragent/AbstractUserAgentAnalyzerDirect.java