The guide will eventually be part of Solr's release when the RefGuide is ready to accommodate it. In the meantime its been designed to be easily read directly from Github.
The guide contains close to 200 visualizations and examples showing how to use Streaming Expressions and Math Expressions for data analysis and visualization. The visual guide is also designed to guide users that are not experts in math in how to apply the functions to analysis and visualize data.
The new visual data loading feature in Solr 8.3 is also covered in the guide. This feature should cut down on the time it takes to load CSV files so that more time can be spent on analysis and visualization.
Re: The Visual Guide to Streaming Expressions and Math Expressions
The visualizations are all done using Apache Zeppelin and the Zeppelin-Solr interpreter. The getting started part of the user guide provides links for Zeppelin-Solr. The install process in pretty quick. This is all open source, freely available software. It's possible that Zepplin-Solr can be incorporated into the Solr code eventually but the test frameworks are quite different. I think some simple scripts can be included with the Solr to automated the downloads for Zeppelin and Zeppelin-Solr.