From Xojo Documentation

Property (As Boolean )
aTextArea.MultiLine = newBooleanValue
BooleanValue = aTextArea.MultiLine

Supported for all project types and targets.

If True, wrap text to multiple lines and allow more than 32K of text.


Changing this property at runtime has no effect.

Page Up, Page Down, Home and End keys are supported for multiline TextAreas. A vertical scroll bar is added automatically when MultiLine is True.

MultiLine TextAreas support any standard terminator (Return, Linefeed, or Return + Linefeed) to indicate the end of a paragraph.