Microwave Bags If You're Not Supposed To Use Plastic Containers In The Microwave, How Are Steamer Bags Safe?

If you're not supposed to use plastic containers in the microwave, how are steamer bags safe? - microwave bags

There is a growing popularity in plastic bags of frozen vegetables in them that can be steamed in the microwave ... Is it safe for you? Because it is generally recognized how dangerous it is to heat something in a plastic container in the microwave, why the FDA allows the sale of these pockets of steam (TV dinners, and many other species that microwave heating is required)?