YAML custom_metadata format in Poster 2

Can someone tell me what is the format for the custom_metadata entry in Poster 2 when using markdown files?

Referenced here:
Blogging with Markdown Files

What are you trying to archive?

The first blog has general content, typically a “how-to” blog.

The second blog contains bibliography items.

Is custom_metadata somehow related to open graph?

TIA
François

No. You’re not able to change the open graph schema Information.