startScroll() will make the text begin scrolling in the direction given by calling setDirection(). If the text is scrolling left to right (GTK_SCROLLINGLABEL_RIGHT), the current character position is set to the end of the text. This means that the last character of the label will be the first character shown. If the text is scrolling right to left (GTK_SCROLLINGLABEL_LEFT), the current character position is set to zero. This means that first character shown will be a blank space.
This method is best used when connected to an event.