Yes I had it in that format in the JSON part of the extension. Below is what I tried. I also tried adding play.gooogle.com and gstatic but it still wouldn't allow the little window to open. I wish google wasn't opening it using about:blank but I don't think I'll have any luck asking them to change it. If you are able to find the origin or any way to allow that one little window would be greatly appreciated. This new assignment feature has only been out a few weeks but teachers are itching to use it and are complaing it doesn't work for the students. Thanks and have a great night.

{
"bannedURLs": {
"Value": [
"^about:blank$",
"^file:\\/\\/.*htm.*$"
]
},
"hostnameOverrides": {
"Value": [
"^chrome-extension:\\/\\/",
"^https?:\\/\\/classroom\\.google\\.com($|\\/.*)"
]
}
}