Based on Codeplex issue https://wpftoolkit.codeplex.com/workitem/21844.
When a Capital letter is placed in the Mask, typing a letter should display a capital letter. The same way, if a regular small letter is placed in the mask, typing a letter should display a regular small letter.
When a Capital letter is placed in the Mask, typing a letter should display a capital letter. The same way, if a regular small letter is placed in the mask, typing a letter should display a regular small letter.