Shiny 1.4.0

This is a companion discussion topic for the original entry at

Shiny 1.4.0 has been released! This release mostly focuses on under-the-hood fixes, but there are a few user-facing changes as well.
If you’ve written a Shiny app before, you’ve probably encountered errors like this:
div("Hello", "world!", ) #> Error in tag("div", list(...)) : argument is missing, with no default This is due to a trailing comma in div(). It’s very easy to accidentally add trailing commas when you’re writing and debugging a Shiny application.