CrossMark identifier

Estudar `[<custom-meta>](https://jats.nlm.nih.gov/publishing/tag-library/1.1/element/custom-meta.html)`

```
...
<article-meta>...
<counts>
<page-count count="1"/>
</counts>
<custom-meta-group>
<custom-meta>
<meta-name>crossmark</meta-name>
<meta-value>2013-02-15T11:32:17</meta-value>
</custom-meta>
</custom-meta-group>
</article-meta>
...
```