code: public void validateExternalBindings() throws Exception {
  		HashSet<String> missingExternals = new HashSet<String>();
  
  		validateExternalBindings(mainContentContainer, missingExternals);
  		hasValidatedExternals = true;
  		// No problem! Validation complete
  		if (missingExternals.size() == 0) {
  			hasValidatedExternals = true;
  		} else { // Error for all missing externals
  
  			StringBuilder join = new StringBuilder();
  			boolean first = true;
  			for (String item : missingExternals) {
  				if (first)
  					first = false;
  				else
  					join.append(", ");
  
  				join.append(item);
  			}
  
  			String message = String.format("ERROR: Missing function binding for external%s: '%s' %s",
  					missingExternals.size() > 1 ? "s" : "", join.toString(),
  					allowExternalFunctionFallbacks ? ", and no fallback ink function found."
  							: " (ink fallbacks disabled)");
  
  			error(message);
  		}
  	}
docs: Check that all EXTERNAL ink functions have a valid bound C# function. Note
  that this is automatically called on the first call to Continue().