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.

We initially considered replacing the table tabs with a list of checkboxes, similar to what is used in the New/Deprecated/Preview API summary pages. However, unlike with releases in API summary pages, it does not make much sense to allow viewing specifications for a subset of host domains. The use case for host selection is to view specifications for one host at a time, and that is made difficult with checkboxes because other items must be deselected before selecting the item to be viewed.

The control element that seems to work best for the External Specifications page is an HTML select element, which is rendered as drop-down menu list.

The original description of this issue also proposed to move the code for selection control to the Table class. Upon further inspection, this does not seem advisable. The checkbox list in summary pages does not pertain to any Table instance, rather it controls entries spread over multiple tables, any of which may not contain a complete set of items. The select element introduced for the External Specifications page, although pertaining to a single Table instance, is specific to this use case in several aspects. There are currently no plans to use it anywhere else, and would need to be much more complex when implemented as a generic feature of the Table class.