This is to pass more parameter to the documentTree velocity macro from the locationPicker velocity macro.
We need it by example here: https://github.com/xwiki-contrib/book-versions/commit/b9af3c76de088d2aa04818bb5408945907e11645#diff-fe2a2389c53f3d1b7046681db9ee06814e9eacd5b07f02091a41fb44e7f82ee3R222-R263