Rule Definition
The point of components is to be small, dynamic, independent and usable anywhere - a stand-alone piece of logic, that receives something, does something and returns something. Binding it to a direct parent destroys the concept of using the component anywhere. In most cases, reaching into the parent makes the application more difficult to debug and understand, especially if parent data is mutated. When looking at that component later, it will be very difficult to figure out where that mutation came from. This is how you keep the dataflow clean and without implicit code.

Remediation
Use custom events and $emit to send emissions to the parent which vue will detect

Violation Code Sample

export default {
props: {
      isSelected: {
             type: Boolean,
             required: true
            }
        },
methods: {
  toggle(){
      this.$parent.isSelected = !this.$parent.isSelected
   }
  }
})

Fixed Code Sample

export default {
props: {
      isSelected: {
             type: Boolean,
             required: true
            }
        },
methods: {
  toggle(){
      this.$emit('input', !this.value)
   }
  }
})

// in parent
<my-component v-model = "value"/>
<my-component :value="value" @input= "(newVal) => {value = newVal}" /> // update on input event

https://vuejs.org/v2/guide/components-edge-cases.html#Accessing-the-Parent-Component-Instance https://vuejs.org/v2/guide/components-edge-cases.html#Accessing-the-Root-Instance