foo.clj

(def percentage-spec (s/conformer #(or (some-> (re-matches #"(-?\d+(\.\d+)?)%" %) (nth 1) Double/parseDouble)
                                     ::s/invalid)
                       #(str % "%")))

(s/def ::absolute-coordinate number?)
(s/def ::pct-coordinate percentage-spec)
(s/def ::coordinate (s/or :abs ::absolute-coordinate
                      :pct ::pct-coordinate))

(def specrec (s/cat :lx ::coordinate
               :by ::coordinate
               :rx ::coordinate
               :ty ::coordinate))

pdfdata.ops> (s/conform ::coordinate 123)
[:abs 123]
pdfdata.ops> (s/unform ::coordinate *1)
123
pdfdata.ops> (s/conform ::coordinate "-50.2%")
[:pct -50.2]
pdfdata.ops> (s/unform ::coordinate *1)
-50.2%
pdfdata.ops> (s/conform specrec [12 "-50.2%" -99.1 "2%"])
{:lx [:abs 12], :by [:pct -50.2], :rx [:abs -99.1], :ty [:pct 2.0]}
pdfdata.ops> (s/unform specrec *1)
(12 "-50.2%" -99.1 "2%")