Replace characters in text: with RegexReplace?

Hello.

I have a sentence "Hello World!".

I would like to replace the characters in position 7 to 10 (that is orld) in my sentence by "ild".

We would get "Hello Wild!".

Anyone know how?

Thank you.

Done this using replace, not regex

https://drive.google.com/file/d/0B2ztlkoVxR-FN2VVOEs4SG8yNTA/view?usp=sharing[/code:sdph7so6]

using RegexReplace the command is RegexReplace(Input.Text,"orld","","ild")

Thank you but this is not what I'm looking for if I replace the phrase "Hello World, this is the world" I get "Hello Wild, this is the wild" but i want "Hello Wild, this is the world".

That's why I want the start and end positions or start and the number of characters selected.

Not sure exactly what you mean, I can only suggest you read up on text expressions here scirra.com/manual/126/system-expressions