Display an insert marker before or after the specified tab item.
A value of -1 will clear the mark.
@param index the index of the item with which the mark is associated or null
@param after true if the mark should be displayed after the specified item
@exception IllegalArgumentException<ul>
</ul>
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Display an insert marker before or after the specified tab item.
A value of -1 will clear the mark.
@param index the index of the item with which the mark is associated or null
@param after true if the mark should be displayed after the specified item
@exception IllegalArgumentException<ul> </ul>
@exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>