"Many packaged foods, particularly the more perishable ones, come with an expiration date. The expiration date represents the food scientist’s best guess on how long a food will last before it spoils. A food scientist calculates the expiration date by first determining the product’s shelf life (how long it will last under typical storage). The expiration date is usually set before the end of shelf life, but it is not as simple as being acceptable to eat the day before the expiration date and unacceptable the day after the date."
About the underlined part above,
1. Does 'it' means 'The expiration date'?
2. Is the 'as' is functioning as a preposition such as 'like'?
3. If I parse the simple sentence - "it is acceptable to eat the day before . . . after the date" has been reduced into the simple phrase - "(it) being acceptable to eat the day before . . . after the date", is this parse justified and then how the "it is" could be done into "(it) being" as a participle phrase?
I would appreciate on your explanation.