@Paul ******
I told you what a re-entry permit it is. It keeps the stamp you have from being cancelled when you leave Thailand. If you leave Thailand without a re-entry permit your visa or extension will be cancelled. A re-entry permit does not give you any extra time in Thailand. It is not an extension. It just keeps your existing stamp alive.
If your extension stamp in your passport ends July 15th and you leave Thailand with a re-entry permit and return on June 1st, you'll be stamped back in on your existing stamp until July 15th. If you leave without a re-entry permit then you have nothing anymore as everything is cancelled. If you leave with a re-entry permit but don't come back by the time your stamp runs out then you also have nothing because you didn't return before your extension expired to apply for a new extension.
It is NOT a multiple entry visa. It is a re-entry permit, either single re-entry or multiple re-entry.