Markdown being a simple format, it does not offer any way to attach additional metadata to a note. The community came up with a solution by inserting a YAML header at the top of each note to contain its metadata. This method is widely supported among Zettelkasten softwares, including `zk`.
```yaml
---
title: Improve the structure of essays by rewriting
All metadata are indexed and can be printed in `zk list` output, using the template variable `{{metadata.<key>}}`, e.g. `{{metadata.description}}`. The keys are normalized to lower case.