The motivation for the two widgets is related. I wanted to add book titles about the World Championship to Mahalo, but their tool, which drags in everything related to the search phrase from Amazon, returned more junk than useful titles. Example: 'World Chess Championship Matches, Vol 2' and 'World Chess Championship Matches. Book 2', both by Berdichevsky, were two separate entries. Then there were three entries for the book on the 1951 Botvinnik - Bronstein match by Wade and Winter.
My problem with widgets is that they often slow down the loading of the page, sometimes to a crawl. If people are going to wait for a page to load, they might as well get something useful.
As long as I've touched on the subject of Berdichevsky, I've sometimes wondered what exactly are these books, spanning three volumes. Schachversand.de has pages on World Chess Championship Matches for Vol.1, Vol.2, and Vol.3, but the reviews are somewhat brief and in German. The preface for Vol.2, written by Smyslov, says,
Here, for the first time, have been collected together all the annotated games of all the matches for the world championship matches between 1886 and 1998. Apart from being an encyclopedia, this work also has considerable instructional value, since at all times people have learned primarily from the games of the champions.
'All the annotated games of all the matches for the world championship'; that's a lot of annotations.