> Because the registry is a database. Why would you put comments in a database?

A database stores whatever data is necessary for the application. If comments for application records are needed, that includes comments.

A self-documenting registry where applications registered user information about keys that they used (whether or not the application populated them) as well as apps populating data for keys, so that navigating to a key in the UI would provide you with the documentation from any app or apps concerned with that key as well as the ability to review and edit the data value would be awesome.

The registry is as much a database as it is a very large config file, and config files, as you've rightly observed, have comments.

Oracle has user/all/dba_tab_comments and user/all/dba_col_comments.

The only places in my legacy databases where these are populated emerged from the Erwin data modeler. We are lazy in not populating them with new tables.

I wonder if SQLite has something similar.

Ms SQL has extended properties, particularly the ms_description one that is exposed in ssms. But that's comments on database columns and objects, not data points.

Which highlights the difference between the registry and an rdbms. In an rdbms you can absolutely comment the columns and tables, just not the rows and individual data points.

In the registry, the data isn't tabular. Every data point has a corresponding field name. That name absolutely would support a comment in sql.