protected void failIfAlreadyBuilt() {
            if (didBuildStep) {
                throw new IllegalStateException(
                    "A builder can provide only a single instance. " +
                    "It is not allowed to set values after doing build()");
            }
        }
This function is used only for analyzing which patterns that could possibly be relevant
were actually relevant for the matcher actions.
@return The list of Matches that were possibly relevant.
analyzer/src/main/java/nl/basjes/parse/useragent/AbstractUserAgentAnalyzerDirect.java