One useful programming convention is to use -1 to mean ‘go to the end of’. For example, the OpusScript function SetSelection allows you to set the number of letters you want to select in a text box

myTextInput.SetSelection(0,-1)

In this example, the whole of the text is selected (i.e. from the first index position to the last).

In the OpusScript function descriptions, you will be advised if and when you can use the -1 programming convention.