Add "regexCheck" for Facebook and Flipboard

Facebook from: https://www.facebook.com/help/409473442437047 but I don't know how to handle this requirement: "They can't contain generic terms or extensions (.com, .net)".
Flipboard from: https://flipboard.helpshift.com/a/flipboard/?s=managing-your-account&f=help-with-username-issues&p=web

data.json

@@ -14,7 +14,8 @@
   "Facebook": {
     "url": "https://www.facebook.com/{}",
     "urlMain": "https://www.facebook.com/",
-    "errorType": "status_code"
+    "errorType": "status_code",
+    "regexCheck": "^([a-zA-Z0-9.]){5,}$"
   },
   "YouTube": {
     "url": "https://www.youtube.com/{}",
@@ -108,7 +109,8 @@
     "url": "https://flipboard.com/@{}",
     "urlMain": "https://flipboard.com/",
     "errorType": "message",
-    "errorMsg": "loading"
+    "errorMsg": "loading",
+    "regexCheck": "^([a-zA-Z0-9_]){1,15}$"
   },
   "SlideShare": {
     "url": "https://slideshare.net/{}",