Cutting Film on Back Glass

Hi guys.
I'm considering tinting my car and was wondering about the defroster lines on the back glass. How is the film cut after being applied on the back glass? Is it shaped with a razor? If so, wouldn't that damage the defroster lines?
Sorry if this sounds ignorant.

Read around. THe film is normally cut on the outside by a professional tinter.

The film is shaped and shrunk on the outside of the glass. Then it is cut with a very sharp stainless steel "olfa" knife to size. It is usually not cut after it is applied, although sometimes there is slight trimming. Nothing is going to damage your defroster lines, unless the installer is very bad for some reason. Your defroster will still work like normal, nothing to worry about.