to.
                            type: string
                          operator:
                            description: operator represents a key's relationship
                              to a set of values. Valid operators are In, NotIn, Exists
                              and DoesNotExist.
                            type: string
                          values:

message LabelSelectorRequirement {
  // key is the label key that the selector applies to.
  // +patchMergeKey=key
  // +patchStrategy=merge
  optional string key = 1;

  // operator represents a key's relationship to a set of values.
  // Valid operators are In, NotIn, Exists and DoesNotExist.
  optional string operator = 2;

  // values is an array of string values. If the operator is In or NotIn,

// returns, won't affect the copy of `func`/`grad` in `g`.
// If `func` or `grad` are already in `g`, TF_GraphCopyFunction has no
// effect on them, but can establish the function->gradient relationship
// between them if `func` does not already have a gradient. If `func` already
// has a gradient different from `grad`, an error is returned.
//
// `func` must not be null.