public Container documentProcessor(String id, String chainName, Class<? extends DocumentProcessor> docproc, ConfigInstance... configs) {
                List<ComponentItem<? extends DocumentProcessor>> chain = docprocs.get(chainName);
                if (chain == null) {
                    chain = new ArrayList<>();
                    docprocs.put(chainName, chain);
                }
                chain.add(new ComponentItem<>(id, docproc, configs));
                return this;
            }
@param id        component id
@param chainName chain name to add docproc
@param docproc   add this docproc to the document processing chain
@param configs   local docproc configs
@return builder
application/src/main/java/com/yahoo/application/Application.java