This is the root directory of the user/project/software AFS HTML pages; 

the existance of this file changes the URL root from 
www.afs.enea.it/userid to www.afs.enea.it/vault_user/userid
www.afs.enea.it/project/project_name to www.afs.enea.it/vault_project/project_name
www.afs.enea.it/software/software_name to www.afs.enea.it/vault_software/software_name