This also serves to provide a page with all the metadata fields present. If you have a dynamic page with a GraphQL query for a metadata field, there must be at least one page with that field present. Otherwise Gridsome throws an error.
Normally category isn't present in the metadata. It's autopopulated by the framework based on where the Markdown file is placed. But this isn't placed in a category, so it's in the metadata here as a workaround.
Inserts
Here's how Inserts are inserted:
This is an example Insert!
Vue components
Using Vue components:
They can even be used 
inline!
Graymatter
Using metadata fields in the content:
Authors: Jose and me