Add support for full configuration of reveal slides in notebook metadata

[bouzidanas]

(Suggested labels: enhancement, feature)

This pull request introduces a new feature that allows reveal.js presentation settings to be configured directly within a notebook's metadata.

Currently, reveal.js options for slide exports are primarily set via command-line arguments or configuration files. This separates the presentation's configuration from its content, making it less portable. For example, if a user wants to share a notebook that is designed to be presented with a specific theme or transition, they must also share the command-line flags needed to reproduce it or edit the html file themselves which requires familiarity with reveal.js. Furthermore, only a limited number of reveal.js options are accessible via the command line and in the configuration files.

This enhancement allows users to embed reveal.js settings within the .ipynb file itself, making presentations self-contained and easier to share and reproduce consistently.

Implementation Details

The feature is implemented by overriding the from_notebook_node method in the SlidesExporter. The new implementation preserves the existing conversion logic by calling super().from_notebook_node(). It also inspects the notebook's metadata for a reveal key and merges the settings with the configuration already loaded from command-line options and defaults.

A clear order of precedence (override order) is maintained to ensure intuitive and predictable behavior:

1. Command-line arguments (highest)
2. Notebook metadata
3. Config file
4. Hard-coded defaults (lowest)

This ensures that users can set project-wide defaults in a notebook but still easily override them from the command line for a specific export.

How to Use

To use this feature, a user can edit the notebook's metadata (e.g., in Jupyter, via Edit > Edit Notebook Metadata) and add a reveal object.

Example Notebook Metadata:

{
  "kernelspec": {
    "display_name": "Python 3",
    "language": "python",
    "name": "python3"
  },
  "language_info": {
    "name": "python",
    "version": "3.9.7"
  },
+ "reveal": {
+   "theme": "night",
+   "transition": "zoom",
+   "scroll": true
+}
}

When a notebook with this metadata is exported using jupyter nbconvert --to slides, it will automatically use the "night" theme and "zoom" transition, unless a different value is provided on the command line.

List of config options

Related Issues

1. Better support for reveal.js functionality #612
2. Is there a simple way to customize Reveal.initialize arguments? #1851
3. Add additional configuration options to SideExporter #849
4. - bump reveal.js #2216 (new config options)

[petrelharp]

This would really help make jupyter a more functional platform for making presentations. Thanks for working on this! Where's the right way to document this - here?

[bouzidanas]

Where's the right way to document this - here?

and also here I think...