A walled garden allows users to only access websites that you designate prior to authenticating through the splash page. This is useful if you want to provide users access to a company website but not give them internet access.
Domains in the format "facebook.com" will be wildcarded: all subdomains of facebook.com will be available. Additionally, the Datto walled garden can support wildcards (e.g., *.open-mesh.com).
Using the format "dev.facebook.com" will only allow access to dev.facebook.com and no other subdomains (www.facebook.com, etc.).