These two methods work together as a way to temporarily save a text range specification and restore it when needed. The getBookmark( ) method returns an opaque string (containing binary data that is of no value to human users). Once that value is stored in a variable, the range can be modified as needed for the script. Some time later, the bookmarked text range can be restored with the moveToBookmark( ) method:

var rangeMark = myRange.getBookmark( );
...
myRange.moveToBookmark(rangeMark);