When you run the above composition and click on the window, the composition displays the coordinates of the point where you clicked.
What does it display before the first click? Perhaps surprisingly, it's Hello World! That's because Hello World! is the default value of the Text input port.
This feature request is to make the port's initial value visible somehow and to make it editable, so you can change it to something other than the default.
Currently, if you want to set an initial value, you have to add some extra nodes. For example, the below composition displays the text nothing yet until the first mouse press.