Defining whitespace

It's funny the little things that need to be properly defined. For example...

There are a few internal functions that know about whitespace. For example, the PARSE function by default will deal with whitespace.

The Question:

What do we mean by whitespace?

Internally in R3, there are 2 definitions:

However, for such functions, do we want to consider other control chars as whitespace? For example, is backspace whitespace?

In R2, many control chars were treated as whitespace, but I am not so sure we want to do that in R3.

Your opinion?