NJW (and other German law journals)

This style is based on the "Juristische Zitierweise (Stüber)" style by Oliver Wolf and Philipp Zumstein
    (https://www.zotero.org/styles/juristische-zitierweise), but the citation is adapted for the style of
    German law journals, such as NJW (Neue Juristische Wochenschrift), MMR (Multimedia und Recht) etc., as follows:
    - Citations are in-text. In German legal journals sometimes citations are used in footnotes, sometimes in-text,
      although the citation itself does not differ. With "in-text", you can choose for yourself and create the
      footnotes yourself using your word-processor if necessary.
    - Citations do not end with ".". The "." is obsolete for in-text citations. Furthermore, citations in German law
      journals are often accompanied by supplemental text and explanations.
    - Commentaries and handbooks should use publication type "entry-encyclopedia". See details below.
    - note that some law journals use slightly different citation
Okay, what I need here is only the number, no additional information.
This should always look like "2. Aufl. 2014".
My solution for now would be to omit the edition and just print the year, if it is not numeric. However, would you have a solution to just pick the number (like a regex ^(\d)* or similar)?
  <macro name="edition-if-available">
    <choose>
      <if variable="edition">
          <choose>
            <if is-numeric="edition">
              <text variable="edition" suffix=". Aufl. "/>
            </if>
          </choose>
          <date date-parts="year" form="text" variable="issued" suffix=", "/>
      </if>
    </choose>
  </macro>