XYZ data in ICC profile


I am new to coding with ICC profiles, and have been heavily into researching the ICC v4 specification for a program I am building.

In the specification (Section 6.3.2), they show these equations:

Xa = (Xmw/Xi)*Xr
Ya = (Ymw/Yi)*Yr
Za = (Zmw/Xi)*Zr

One question I have is that I understand how and where (what address) to find in an actual profile the values for XYZa, XYZmw and XYZi. But there is no discussion on where XYZr data is located. Is this data not in the profile? it actual XYZ values calculated from the color data for each pixel in an image, for instance?

Thanks for any replies!