In ActionScript, each compilation unit contains exactly one declaration that is visible from the outside. In TypeScript modules, it is possible to export multiple identifiers, but there is a default export, so when converting code from ActionScript, it is straight-forward to use this default export to export the primary declaration of the compilation unit, usually a class.

While it is possible to combine the declaration and the (default) export of a class, the conversion tool does not do so, because later you'll see cases where that is not possible or more redundant. So for consistency, the conversion tool always ends each source file with the default export:

default export Foo;