Spell check feature is desired in all free-text user input fields like TextBox, Text Area and Rich Text Editors.
By default, spell check is available only in text box and text area controls. The highlighting of misspelt words ‘as-you-type’ is not available on Rich Text Area controls.
If a spell check action is used for the Rich Text Editor Control, on events like Focus or, if a harness-level button is used to trigger the OOTB spell check, UI disruption is observed especially on Multi-Select Controls.
Harness level button was placed as per the suggestions in the following link