code: function processYAMLVariable(v, lvl, indent) {
  
      // Scalars
      if (typeof v === 'string')
        return yml.string(v);
      else if (typeof v === 'number')
        return yml.number(v);
      else if (typeof v === 'boolean')
        return yml.boolean(v);
      else if (typeof v === 'undefined' || v === null || isRealNaN(v))
        return yml.nullValue(v);
  
      // Nonscalars
      else if (isPlainObject(v))
        return yml.object(v, lvl, indent);
      else if (isArray(v))
        return yml.array(v, lvl);
      else if (typeof v === 'function')
        return yml.fn(v);
  
      // Error
      else
        throw TypeError('artoo.writers.processYAMLVariable: wrong type.');
    }
docs: Get the correct handler corresponding to variable type