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If there is just one `Input` I suppose I could call `String.Format()` inside an `.Apply()` on that input.

But in my case there are multiple `Input` that each correspond to a placeholder in the composite format string.

Right - the answer is effectively always `.Apply`.  And if you have multiple inputs `.All().Apply()`.  Other things (like `Output.Format`) are effectively all just sugar for common cases - but if your case falls outside of those - you want `.Apply` and maybe `.All`.

Thanks <@UB3BGTV63>! It’s all slowly beginning to make sense.

```var a = Output.Create("a");
var b = Output.Create("b");
var c = "{0}+{1}";
var d = Output.All&lt;string&gt;(a, b).Apply(vs =&gt; string.Format(c, vs.ToArray()));```

Makes perfect sense <@UB39JFCKC> - thanks!