GitLab pages project name as path? (mywebsite.com/projectname)

When using GitLab pages to host a project website, is it possible to have it’s url be something like www.mywebsite.com/projectname ?

When trying to add that as a domain (using “New Domain” in the pages settings page), it says you can’t use / as a character.

Or is it only possible to add them as a subdomain in your dns? ( projectname.mywebsite.com for instance).

Note: I asked this same question on Stackoverflow but got no response there: https://stackoverflow.com/questions/53523390/gitlab-pages-project-name-as-path-mywebsite-com-projectname

Thanks!