[Property] importance [Values] 0 (min) 1 (max) [Description] 
Estimated importance of a role to completion of the main tasks of a delivery unit. For example a main menu is typically required for a user to beale to completer the main tasks of a site. A secondary side menu is typically less important. Hence a main menu has an importance level of one and secondary side menu may have an importance level of 0.6.