The `External Specifications` page provides a table of references to external specifications, grouped by the host domain, which is effectively an open-ended set that may grow over time as new specs are referenced.

The ability to replace table tabs with a checkbox list was developed in parallel with the `ExternalSpecsWriter` but is currently specific to the "New In ..." kind of pages.

It would be nice to refactor the code to filter a table with checkbox list, so that it can also be used on the External Specifications page. One obvious suggestion is to refactor the code into the `html.Table` class, which is where the tabs are currently implemented/supported.