Spork says it accepts YAML on slides. It isn't really YAML - it's an undocumented format that looks really similar to YAML.

The files ~/.sporkrc/config.yaml, your-presentation/config.yaml, and your-presentation/config/config.yaml are all parsed differently. You can specify plugin_classes in your ~/.sporkrc/config.yaml. It will throw errors if you try to do the same thing from your-presentation/config.yaml. I didn't try setting it in your-presentation/config/config.yaml

Here's a short explanation of the Spork::Hilite format. The line # to affect follows every hilite expression. The hiliting matches characters by spacing out horizontally. Use the + suffix on a color to indicate that the hilite should apply to the entire line.

.hilite
  This entire line
  Just the word the
+
  g+ 1
        rrr      rrr 2
.hilite
[download]

This entire line
Just the word the