Classes
 ClassDescription
 _Fixation Internal Fixation Node Class Contains all information and related operations on a fixation.
 _Gaze Internal Gaze Node Class Contains all information and related operations on a gaze.
 _Interval Interval Class eye x,y coordinate information during one fixation interval.
 _Message 
 _Root Internal Root Node Class Contains all information of a Experiment Tree.
 _Saccade Saccade Node Class Contains all information and related operations on a saccade.
 _Trial Internal Trial Node Class Contains all information and related operations on a trial.
 _Voice 
 _Word Internal Word Node Class.
 Node Abstract node class includes basic operation to build data tree and maintenance the node relationship.