message: clarified that name is a required field in an attribute
diff: @@ -46,9 +46,10 @@ package onnx;
  // A named attribute containing either singular float, integer, string
  // and tensor values, or repeated float, integer, string and tensor values.
  -// An AttributeProto should contain the name field, and *only one* of the
  +// An AttributeProto MUST contain the name field, and *only one* of the
  // following content fields, effectively enforcing a C/C++ union equivalent.
  message AttributeProto {
  + // The name field MUST be present for this version of the IR.
  optional string name = 1; // namespace Attribute
  optional float f = 2; // float
  optional int64 i = 3; // int
  