insert

This variable inserts contents of items variable into another item or items.

Yaml:

# Example
- insert: main
  items:
  - STONE
  - DIRT

- stack: LIME_WOOL
  id: myMenu

# Example 2
- insert: 
  - main
  - $myMenu # it will be inserted to current end of this category
  - $myBlock # it will be inserted to start of this category on its initialization
  items:
  - STONE
  - DIRT

- stack: GLOWSTONE
  id: myBlock

Groovy:

inventory {
  // Example
  insert ('main') {
    item('STONE')
    item('DIRT')
  }

  item('LIME_WOOL') {
    id '$myMenu'
  }

  // Example 2
  insert ([
    'main', 
    '$myMenu', // it will be inserted to current end of this category
    '$myBlock' // it will be inserted to start of this category on its initialization
  ]) {
    item('STONE')
    item('DIRT')
  }

  item('GLOWSTONE') {
    id 'myBlock'
  }
}