slot

Used on content inserted into child components to indicate which named slot the content belongs to. - Vue.js guide

MyCustomComponent.vue

<template>
  <slot name="main">
    <span>This is the default main slot text</span>
  </slot>
</template>

MyForm.vue

...

<script>
export default {
  data() {
    return {
      uiSchema: [{
        component: 'my-custom-component' // globally registered component
        children: [{
          component: 'div',
          fieldOptions: {
            domProps: {
              innerHTML: 'This child component will occupy the main slot of the parent'
            }
            slot: 'main'
          }
        }]
      }]
    }
  }
}
</script>