The @key attribute is used within the <ft:meta> element to define the name of the metadata to apply to a map or a topic. It must be the same name as that used in the content.
The @key attribute is mandatory within the <ft:meta> element.
The following lines show an example of the @key attribute:
<?xml version="1.0" encoding="UTF-8"?>
<ft:map ...>
...
<ft:metas>
<ft:meta key="product" type="string">myProduct</ft:meta>
...
</ft:metas>
<ft:toc>
<ft:node originId="192fe" ft:title="Introduction" href="intro/introduction.html"
type="topic">
<ft:metas>
<ft:meta key="product">myProduct</ft:meta>
<ft:meta key="audience">beginner</ft:meta>
</ft:metas>
</ft:node>
...
</ft:toc>
</ft:map>