How do I limit a query to a certain taxonomy?

You can use taxonomy and terms to get posts from a certain taxonomy term.

<Loop type=post taxonomy=category terms="hello">

For a more detailed description, please see the list of query parameters from the documentation page Loop: Post, and search for the word “taxonomy”. There are some related parameters like taxonomy_compare and taxonomy_relation.

I was thinking it’d be nice to have a shortcut for querying by one or more categories (or tags), and it already exists: the category and tag parameters.

So the example can be simplified to:

<Loop type=post category="hello">