e.errText vs. e.toString

Here's a stupid question...

What is the difference between e.toString() and e.errText?

I've seen examples in Tools Bookshelf where their catch block contains 4 different variations.  Which is best practice to use and what is the difference?

1. TheApplication().RaiseErrorText(e.toString())

2. TheApplication().RaiseErrorText(e.errText())

3. TheApplication().RaiseErrorText(e.toString() + e.errText() );

4.

if(e.errText == null)

{

  TheApplication().RaiseErrorText(e.toString());

}

else

{

  TheApplication().RaiseErrorText(e.errText);

}

I know that the Exception object sets\uses the errText property?  Is that just for system errors and not when I write code to RaiseErrorText?  I'm so confused and could not find clear definition in Siebel\Oracle bookshelf.