From Xojo Documentation
The text displayed.
Assigning a string to the Value property replaces the entire contents of the control. The font, size, and color are uniform and match the values last set with the TextFont, TextSize, and TextColor properties, or if these haven't been used, the settings in the IDE.
Please note that the implementation of the TextField and TextArea controls is platform dependent. Do not expect that the text you assign is the same as the text you receive from this property. For example on Mac your text is converted to UTF-8 internally. On Windows all text after a null character (which means chr(0) and not "0") is ignored. End of line characters can change to their platform specific counterpart. Special characters with Asc values below 32 may be ignored or removed.
Clear (remove) any text that is displayed in the TextArea:
TextArea1.SelectionLength = 10
TextField1.Value = TextArea1.SelectedText