How to use in VerifyAccessToken?

[#1]

In Generate Access token policy,I can set custom attributes as below,

<Attributes> <Attribute name="username" ref="request.formparam.username" display="true"/> </Attributes>

And this attribute is seen in the Accesstoken response.

In Verify Access token policy,there is <Attributes> tag present.Please suggest what is the purpose of this tag.And how to use this tag.I could not get the details from this link.