import ( "github.com/goadesign/goa" "github.com/goadesign/goa/design" "github.com/goadesign/goa/dslengine" ) // ValidateUserPayload validates the input payload for the "create user" endpoint func ValidateUserPayload(payload interface{}) *goa.ErrorResponse { var errs dslengine.ValidationErrors err := design.ValidatePayload(payload, "createUserPayload", &errs) if err != nil { return goa.NewErrorResponse(errs.Merge(err.(*dslengine.ValidationErrors))) } return nil }In this example, the `ValidateUserPayload` function takes a payload and validates it using the `design.ValidatePayload` function from the `github.com/goadesign/goa/design` package. Any validation errors are captured in a `ValidationErrors` instance. If `err` is not `nil`, it means there was an error while validating the payload, so the function creates a new `goa.ErrorResponse` instance using the `ValidationErrors` from both `errs` and `err.(*dslengine.ValidationErrors)`. This way, all the validation errors are captured and returned to the client as a single response. Overall, the `goa.dslengine` package provides useful utilities for validating and merging errors specific to the `goadesign/goa` library.