Topic-Lesson-Choice-Response-Prompt (TLCRP) "tolchorp" format version 0.4,
mediatype text/tlcrp. It is not YAML but is similar:

// example

%tlcrp
topic: tolchorp example
 level: 1 // CEFR A1
 lesson: format
   level: 6 // CEFR C2
   choice: Are you enjoying the demonstration?
     media: beep.mp3
     mediatype: audio/mp3;text=filename
     response: {affirmative}
       result: good
     response: {negative}
       result: bad
     response: what
       result: Are you enjoying the demonstration?
       freeform: true
   choice: good
     media: Excellent!
   choice: bad
     media: I'm sorry to hear that.
prompt: {affirmative}
  words: yes|yeah|sure|ok|fine|ja|si
prompt: {negative}
  words: no|nah

// format

[%tlcrp] // this text following two slashes is a comment

topic: text [{name}] // text with optional name in braces
  level: _ // 1 means A1, 6 means C2

  lesson: text [{name}] // text with optional name in braces
    // optional level (default is topic's)

    choice: question [{name}] // text with optional name in braces
      // body of choice unnecessary if same text (and name) is defined elsewhere
      // optional activity (text e.g. "assignment <URL>"), disabled (true/false),
      //   proofread (as past tense adjective: default true=good, false=iffy),
      //   media (text, file descriptor or base64), mediatype, and level

      response: prompt display text [{name}]
        result: [choice question text and/or name] // final state if missing
        // optional terminal (true means next choice is last; default is false),
        // activity (e.g. "assignment <URL>"), action (e.g. "[%python\n]..."),
        // plus as below for unnested prompts.
      [response...]
    [choice...]
  [lesson...]
[topic...]

// optional unnested items:

topic: text [{name}]
  level: _ // 1 means A1, 6 means C2
  lesson...

lesson: text [{name}]
  // optional level (default is topic's)
  choice...

choice: question [{name}]
  // body of choice unnecessary if same text (and name) is defined elsewhere
  // optional activity (text e.g. "assignment <URL>"), disabled (true/false),
  //   proofread (as past tense adjective: default true=good, false=iffy),
  //   media (file descriptor or base64), mediatype, and level
  response...

response: prompt display text [{name}]
  result: [choice question text and/or name] // final state if missing
  // optional terminal (true means next choice is last; default is false),
  // activity (e.g. "assignment <URL>"), action (e.g. "[%python\n]..."),
  // plus as below for unnested prompts.

prompt: display text [{name}]
  // optional language (default: en), words (default from display text),
  //   media (file descriptor or base64), level, phonemes (default from words),
  //   and freeform (default is false: no keyword spotting)

// end mediatype text/tlcrp