title: Validating a URL
body: <p>Is there a way to validate that an input URL is valid? For example, I've created a sheet that uses information from a different sheet we'll call 'A', but it changes to a new sheet we'll call 'B' every month. I've created an alert that requests the user to input a new URL at the beginning of the month, but how do I check to make sure it's a valid site before trying to pull data from it?</p>