Brett on 18 Sep, 2017 03:47 PM
It uses the system dictionary for spelling and grammar. It will use
whatever dictionary is installed, and can detect language on a
per-paragraph basis, defaulting to the system language.
The reason it's an in-app purchase is by default a web view can't be
spell-checked. It took a massive amount of effort to bring the default
macOS capabilities to the Marked preview, so I've attempted to recoup
some of the time. There's a possibility I make it a built-in feature in
the future, mostly due to complications with the Paddle version of
in-app purchases (which, by the way, are currently not working, so if
you're interested in purchasing, wait until after the next update).