In this episode, Tyler demonstrates the VoiceOver Text Checker on macOS, a feature that identifies common errors in typed text such as misspellings, repeated spaces, and misplaced capital letters.
This feature can be accessed via Keyboard Commander, and by default is mapped to the letter D. When in a text field, pressing this command should present menus for the types of errors identified in the text, such as misspellings, white space, etc.
At the time of posting, this feature has several bugs, such as not always identifying errors even when they are present, spelling suggestions not being present in the context menu when selecting a misspelled word, and the left and right arrow keys moving by word instead of character after selecting an error from one of the menus. These issues seem to occur inconsistently, and different users report different experiences with this feature, so your individual results may vary. Apple has been made aware of all these issues, and you can find further discussion of them in this AppleVis forum thread.