Document limitation of self-contained with Pandoc

[cderv]

It seems there are several cases to consider. This issues aims to compile the different one we found:

• data-background is not to be used: use the long form as documented https://revealjs.com/backgrounds/

  • Background images do not work with self contained documents #39
  • background images not found when using output_dir #54

• Seems like pandoc won't encode a global setting passed in YAML header

  • Limitation of Pandoc ?
    • background-image in YAML metadata is not embedded as base64 in self-contained reveal.js jgm/pandoc#5124
  • But would a data URI works in reveal.js initialization parameter ?
    • https://revealjs.com/backgrounds/#parallax-background

• Some attributes are not base64 encoded by Pandoc (yet ?)

  • data-background-video: This attributes is transformed as <video> tag by reveal.js. This element has src= so it usually gets picked up by Pandoc, but not in this case because of JS post processing.
  • data-background-iframe: This is transformed by revealjs as an <iframe> element. This element has data-src= so it usually gets picked up by Pandoc, but not in this case because of JS post processing.

• Base64 encoded URI in data-background-image are not working for reveal.js 4.1.1 to 4.1.3.

  • Update to next reveal release for self-contained and background-image to work #137