why is :foo not working

core.clj

(ns zip-fail.core
     (:require
      [clojure.xml :as c-xml]
      [clojure.data.xml :refer [parse parse-str]]
      [clojure.zip :refer [xml-zip]]
      [clojure.data.zip.xml
       :refer [xml-> xml1-> attr text= attr= text]]))


(def xml "<foo id = \"qix\">bar</foo>")

(def z (-> xml parse-str xml-zip))

(xml-> z
       (text= "bar")
       text)
;=> ("bar")

(xml-> z
       (attr= :id "qix")
       text)
;=> ("bar")

(xml-> z
       :foo)
;=> ()


#_(defproject zip-fail "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.8.0"]
                 [org.clojure/data.csv "0.1.3"]
                 [org.clojure/data.zip "0.1.1"]
                 [org.clojure/data.xml "0.0.8"]])