Making "Backspace"
First thing which probably will come into your head is: "How do I delete characters?"
Here we need to apply a little trick :)
For example, we have source text = "Hello world".
Its length is = 11.
To determine the length of text, use len(text)
Essence of our trick: we will take all len(text)-1 symbols in text. So it will take original text, but without last symbol.
left(source.text,text.length) will help us.
For more details see here:
https://www.scirra.com/manual/78/expressions