bootstrap-vue/src/mixins/form-custom.js

BootstrapVue provides one of the most comprehensive implementations of Bootstrap 4 components and grid system for Vue.js and with extensive and automated WAI-ARIA accessibility markup.

export default {
  computed: {
    custom () {
      return !this.plain
    }
  },
  props: {
    plain: {
      type: Boolean,
      default: false
    }
  }
}