Question re Beginning iPhone 3 Development (Mark LaMarche) - Page 312

Hi all,
I wonder if anyone could help me understand the purpose of the following code on page 312 of the book :
if (textFieldBeingEdited ==textField)
textFieldBeingEdited = nil;
The explanation on page 312 says :
"If the field we're using is the one that is currently being edited, that's an indication taht the value we're holding in textFieldBeingEdited is no longer valid, so we set textFieldBeingEdited to nil."
I've looked at this sentence upside down and backwards but I can't work out what this code is for.
Thanks all,
Martin

nil: Zero, non-existant
wiped out... an ex-value...gone - waiting for the new value that may be input by the user.

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