Sets the default \H numbered argument argument of the toplevel headers of each source file.
Note that since the option is inherited by descendants, this can also affect the rendering of ancestors. contains a proposal to instead inherit this property across includes.
If you set this ourbigbook.json option:
  "h": {
    "numbered": true
it is possible to override it for a specific file with and explicit =0 \H numbered argument:
= Not numbered exception

== Child also inherits not numbered
Make every link to something that is not on the current page open on a new tab instead of the current one, i.e. add target="_blank" to such links.