I've released a #Haskell package called pandoc-query. It defines a simple language for querying a collection of #Pandoc documents and formatting the output. It also provides a way to embed queries in a Pandoc document, so that when the document is converted to a new format, the query is replaced with the results. I developed this as part of a project to create a custom #PKM. I looked at Obsidian, LogSeq, Zettlr, AnyType, among others, but none of them met my needs, so I wrote this package as part of an ad hoc solution.