How to get MutationHookResult?
import MutationHookResult from 'fontoxml-blueprints/src/MutationHookResult.js'
Represents the result of a mutation hook.
Any mutation hook may disable any operation by returning MutationHookResult.notAllowed(). Unlike CustomMutationResult, mutation hooks can not affect the active state of the operation, as this state only makes sense in the context of the specific operation that is being run, and a mutation hook does not have access to that information.
Indicates the current operation should not be allowed in the current situation.
Any changes made to the blueprint or selection, either by the mutation hook or by any other participant in the operation, will be ignored.
Indicates the changes in the blueprint and/or selection should be applied to the document, provided the result is valid.