Renting primary residence and taxes

Thanks. I was reading subsection 2.48 of

It talks about defering the tax but I'm not sure: "The taxpayer may instead, however, defer recognition of any gain to a later year by electing under subsection 45(2) to be deemed not to have made the change in use of the property."

What makes it a principal residence? Should I have physically moved in? I'll be renting it probably a month after closing. so it is my principal residence before it was rented, right?

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