From Tobias / Slack channel:
 
We can also add topic and product information to add context to the results, this works similarly to the content type meta tag that you have, example:Current meta-tag for this content:
<meta name="rhd:node-type" content="api_docs" data-react-helmet="true">
If we added an additional meta tag:
<meta name="rhd:taxonomy-topic" content="API Management">
The content would also be added to the topic filter options, which might be a useful enhancement for your content.This is the format for the product meta tag, which would show under the product filter:
<meta name="rhd:taxonomy-product" content="Red Hat OpenShift API Management">
Both product and topics can have multiple tag, example (attached)
 
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Product + Topic doc: https://docs.google.com/spreadsheets/d/1MlucOdKMSnv00nJMjSfTe6VOro3CdBvma-hiCr2Mid8/edit#gid=0