CatchAll.cs

var sourceBlock = new BufferBlock<string>();
var urgentBlock = new ActionBlock<string>(msg => Console.WriteLine($"URGENT: {msg}"));
var normalBlock = new ActionBlock<string>(msg => Console.WriteLine($"Normal: {msg}"));
var unhandledBlock = new ActionBlock<string>(msg => Console.WriteLine($"Unhandled: {msg}"));

// Specific conditions first
sourceBlock.LinkTo(urgentBlock, new DataflowLinkOptions { PropagateCompletion = true },
    msg => msg.StartsWith("URGENT:"));

sourceBlock.LinkTo(normalBlock, new DataflowLinkOptions { PropagateCompletion = true },
    msg => msg.StartsWith("INFO:"));

// Catch-all for everything else - no predicate
sourceBlock.LinkTo(unhandledBlock, new DataflowLinkOptions { PropagateCompletion = true });