Released Specter 1.0.3 https://github.com/nathanmarz/specter/blob/master/CHANGES.md

(setval (index-nav 3) 1 [:a :b :c :d :e])
;; => [:a :d :b :c :e]

(select INDEXED-VALS [:a :b :c])
;; => [[0 :a] [1 :b] [2 :c]]

(setval [INDEXED-VALS FIRST] 0 [:a :b :c :d])
;; => [:d :c :b :a]

(setval (before-index 2) :a '(0 1 2 3 4))
;; => (0 1 :a 2 3 4)