How to use a custom variable from _quarto.yml in templates?

[ThierryO]

With version 1.1.189 we could add custom variables to the book settings in _quarto.yml and use them in the template. The example below provided $book.reportnr$ in the template.

book:
  title: my title
  reportnr: 99999

After upgrading to version 1.2.313 this results in an error property name reportnr is invalid. How can we pass custom variables to a template in an extension?

[cscheid]

The book field has a schema, but other parts of the namespace do not. I believe, for example, that you should be able to use the top level. I do agree that we should do a better job of documenting this (and explicitly documenting, eg, a portion of the namespace that we promise to never have a schema)

[ThierryO]

Placing the custom variable in a different portion works. Downside is that some metadata (title, author) is in the book portion of the namespace, while the custom meta data is in a differrent portion.

book:
  title: my title
  author: me
  output-file: cool-report
  downloads: [pdf, epub]
  sharing: [twitter, linkedin, facebook]

myreport:
  reviewer: myself
  reportnr: 9999

Would I run into problems when moving some metadata from the book portion to the myreport portion? Replacing $book.title$ with $myreport.title$ in the template is obviously not a problem.

book:
  output-file: cool-report
  downloads: [pdf, epub]
  sharing: [twitter, linkedin, facebook]

myreport:
  title: my title
  author: me
  reviewer: myself
  reportnr: 9999

[cscheid]

Templates use the metadata. So those entries will only be accessible to templates if they know where to find them. As an example, myreport.title might be accessible to you, but won't necessarily be accessible to templates that want the book title.

If you need to manipulate metadata at a lower level, you should use Lua filters. Be aware, though, that this happens after validation, so if you change the metadata in a way that breaks the expected schema, you will get relatively obscure errors.