code: function processSubLanguage() {
      var explicit = typeof top.subLanguage === 'string'
      var subvalue
  
      /* istanbul ignore if - support non-loaded sublanguages */
      if (explicit && !languages[top.subLanguage]) {
        return addText(modeBuffer, [])
      }
  
      if (explicit) {
        subvalue = coreHighlight(
          top.subLanguage,
          modeBuffer,
          true,
          prefix,
          continuations[top.subLanguage]
        )
      } else {
        subvalue = autoHighlight(modeBuffer, {
          subset: top.subLanguage.length === 0 ? undefined : top.subLanguage,
          prefix: prefix
        })
      }
  
      // Counting embedded language score towards the host language may be
      // disabled with zeroing the containing mode relevance.
      // Usecase in point is Markdown that allows XML everywhere and makes every
      // XML snippet to have a much larger Markdown score.
      if (top.relevance > 0) {
        relevance += subvalue.relevance
      }
  
      if (explicit) {
        continuations[top.subLanguage] = subvalue.top
      }
  
      return [build(subvalue.language, subvalue.value, true)]
    }
docs: Process a sublanguage (returns a list of nodes).