---
address: common.periodical.issn
description: ISSN (7-digit base + mod-11 check, weights 8..2, 10 -> X)
generator: tdc
---
<sequence name="base"><gen type="regex" value="[0-9]{7}"/></sequence>
<sequence name="issn"><compute>
  <let name="sum">
    <reduce>
      <over><field name="base"/></over>
      <init><int v="0"/></init>
      <do><add><acc/>
        <multiply><current/><subtract><int v="8"/><current_index/></subtract></multiply>
      </add></do>
    </reduce>
  </let>
  <let name="c"><mod><subtract><int v="11"/><mod><use name="sum"/><int v="11"/></mod></subtract><int v="11"/></mod></let>
  <result><concat><field name="base"/>
    <choose>
      <when><test><equals><use name="c"/><int v="10"/></equals></test><then><str v="X"/></then></when>
      <otherwise><use name="c"/></otherwise>
    </choose>
  </concat></result>
</compute></sequence>
<data>${{issn}}</data>