Returns the widget content starting at start for length characters.
@param start offset of the first character in the returned String
@param length number of characters to return
@return widget content starting at start and extending length characters.
@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>
@exception IllegalArgumentException <ul>
<li>ERROR_INVALID_RANGE when start and/or length are outside the widget content</li>
</ul>
Returns the widget content starting at start for length characters.
@param start offset of the first character in the returned String @param length number of characters to return @return widget content starting at start and extending length characters. @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> @exception IllegalArgumentException <ul> <li>ERROR_INVALID_RANGE when start and/or length are outside the widget content</li> </ul>