docs: void sealAndInitialize(FhirContext theContext, Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> theClassToElementDefinitions) {
  		for (BaseRuntimeChildDefinition next : myExtensions) {
  			next.sealAndInitialize(theContext, theClassToElementDefinitions);
  		}
  
  		for (RuntimeChildDeclaredExtensionDefinition next : myExtensions) {
  			String extUrl = next.getExtensionUrl();
  			if (myUrlToExtension.containsKey(extUrl)) {
  				throw new ConfigurationException("Duplicate extension URL[" + extUrl + "] in Element[" + getName() + "]");
  			}
  			myUrlToExtension.put(extUrl, next);
  			if (next.isModifier()) {
  				myExtensionsModifier.add(next);
  			} else {
  				myExtensionsNonModifier.add(next);
  			}
  
  		}
  
  		myExtensions = Collections.unmodifiableList(myExtensions);
  	}