This is an application that utilizes both the current production API from NCBI (at https://eutils.ncbi.nlm.nih.gov/entrez/eutils/) as well as the test version (at https://eutilspreview.ncbi.nlm.nih.gov/entrez/eutils/) to illustrate how the "new" version of Automatic Term Mapping can change what a given search does.
See it in action at: https://esperr.github.io/mapping-tester/
For more PubMed visualization fun, be sure to check out https://github.com/esperr/mesh-subhead-graph, https://github.com/esperr/pubvenn, https://github.com/esperr/pubmed-by-year and https://github.com/esperr/search-workbench