Sets the start position of a Range.
The setStart method takes the following parameters:
startNode startOffset An integer greater than or equal to zero representing the offset for the start of the Range from the start of startNode.
If the startNode is a Node of type Text, Comment, or CDATASection, then startOffset is the number of characters from the start of startNode. For other Node types, startOffset is the number of child nodes between the start of the startNode.