projecttitle in folio numbering

I'd like to have the project title in my folio name.

Example:
Project title: RK_01

Folio numbering:
Text: =%projecttitle+
Text: A/
number format 1: 0

Output result of the folio name: =%projecttitle+A/1
Expected output for the folio name: =RK_01+A/1

I tried to use the %projecttitle and %{projecttitle} but neither works.
I guess the variable %projecttitle is not available in the folio autonumbering... am I correct?
I think it would be nice to have it available.