How can i feed many category?

[CallMeSoul]

when i mine item has many category:

<item>
  //  ...
  <category domain="https://callmesoul.cn/categories/mysql/">mysql</category>
  <category domain="https://callmesoul.cn/tags/frontend/">frontend</category>
  <enclosure url="https://callmesoul.cn/../images/sequelize.jpg" type="image/*"/>
</item>

but i use rss-feed-emitter has only one:

{
  // ...
  categories: [ 'mysql' ],
  enclosures: [],
}