CSL validation error on variable="type"

gistfile1.txt

<?xml version="1.0" encoding="utf-8"?>
<style xmlns="http://purl.org/net/xbiblio/csl" class="in-text" version="1.0" demote-non-dropping-particle="sort-only" default-locale="en-US" page-range-format="expanded">
  <info>
    <title>Helios Short</title>
    <id>http://www.zotero.org/styles/helios-short</id>
    <link href="http://www.zotero.org/styles/vancouver" rel="self"/>
    <link href="http://www.nlm.nih.gov/bsd/uniform_requirements.html" rel="documentation"/>
    <author>
      <name>Susan Thorp</name> 
      <email>susan.thorp@heliosmedcomms.com</email>
    </author>
    <contributor>
      <name>Rob Nicholson</name>
      <email>rob.nicholson@heliosmedcomms.com</email>
    </contributor>
    <category citation-format="numeric"/>
    <category field="medicine"/>
    <summary>This is the standard Helios short house style for citations.</summary>
    <updated>2018-04-06T16:27:00+00:00</updated>
    <rights license="http://creativecommons.org/licenses/by-sa/3.0/">This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License</rights>
  </info>

  <!-- Author: render the author string -->
  <macro name="author">
    <names variable="author" suffix=". ">
      <name sort-separator=" " initialize-with="" name-as-sort-order="all" delimiter=", " delimiter-precedes-last="always"/>
	  <label form="short" prefix=", "/>
      <substitute><names variable="editor"/></substitute>
    </names>
  </macro>

  <!-- Defines the layout of the citation -->
  <citation collapse="citation-number">
    <sort>
      <key variable="citation-number"/>
    </sort>
    <layout delimiter="," vertical-align="sup">
      <text variable="citation-number"/>
    </layout>	
  </citation>

  <!-- Format #1, article-journal -->
  <macro name="format1">
    <text variable="container-title" form="short" strip-periods="true"/>
	<group prefix=" " delimiter=";">
      <date variable="issued"><date-part name="year"/></date>
	  <group delimiter=":">
		<text variable="volume"/>
		<text variable="page"/>
	  </group>
	</group>
  </macro>

  <!-- Format #2, chapter -->
  <macro name="format2">
	<text value="Not finished yet!"/>
    <!-- <text variable="container-title" form="short" strip-periods="true"/> -->
	<!-- <group prefix=" " delimiter=";"> -->
      <!-- <date variable="issued"><date-part name="year"/></date> -->
	  <!-- <group delimiter=":"> -->
		<!-- <text variable="volume"/> -->
		<!-- <text variable="page"/> -->
	  <!-- </group> -->
	<!-- </group> -->
  </macro>

  <!-- Defines the layout of the bibliography -->
  <bibliography delimiter-precedes-et-al="always" et-al-min="3" et-al-use-first="1" second-field-align="flush">
    <layout>
      <text variable="citation-number" suffix=". "/>
	  <text macro="author"/>
	  <choose>
		<if type="article-journal" match="any"><text macro="format1"/></if>
		<else-if type="chapter" match="any"><text macro="format2"/></else-if>
		<else><text value="Type not supported: "/><text variable="type"/></else>
	  </choose>
    </layout>
  </bibliography>

</style>