RichTextBox for UWP supports as-you-type spell checking with a wavy, red underline that highlights misspelled words.

The end-user may right-click the mistake in the document to see a menu with options that include selecting one of the correction suggestions. Users can also choose to ignore the misspelled word or to add it to the dictionary.

Spell checking is done using the C1SpellChecker component, which is included in ComponentOne Studio UWP Edition. 

There are 4 steps for adding spell-checking to your application.

1. Declare a new C1SpellChecker control.
2. Assign C1SpellChecker to the SpellChecker property of your C1RichTextBox control.
3. Obtain the stream for your resource file.
4. Load the MainDictionary of your choice. 

To add spell-checking to your application, see the Adding Spell Checking Task-Based Help topic. 

Dictionary Support

RichTextBox for UWP supports 22 different, customizable dictionaries.