MSDN учит нас, что стандартный Rich Edit поддерживает установку позиций табуляции (начиная с версии 3.0):
EM_SETTABSTOPS Message
The EM_SETTABSTOPS message sets the tab stops in a multiline edit control. When text is copied to the control, any tab character in the text causes space to be generated up to the next tab stop.
This message is processed only by multiline edit controls. You can send this message to either an edit control or a rich edit control.
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Remarks
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Rich Edit: Supported in Microsoft Rich Edit 3.0 and later. For information about the compatibility of rich edit versions with the various system versions, see About Rich Edit Controls.