It select vertices, lines and faces on the view. Several method for selection can be switched.
It selects a vertex, line or face normally.
You can select or deselect continually with 
dragging of left button. (Cannot
select a line.)
It selects joined vertices, lines and faces with a clicked vertex or face are selected or unselected. (Cannot select a line.)
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| Click the face | All faces connected with the clicked face are selected |
Click a line, and it selects or unselects belted vertices and faces. It selects lines when the [Fc] button in the edit option is not pushed.
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| Click the line | Faces are selected like a belt |
It continuously selects lines joined to the clicked or dragged line. When the line has been clicked, lines from the clicked to the farthest are selected together. When the line has been dragged, it selects while gradually spread.
It selects vertices, lines or faces while gradually spread by dragging.
Please click two or more vertices, lines or faces. And vertices, lines or faces on the shortest path through the clicked points are selected. Please 
click a right button or double click when you want to finish the selection.
The vertices traced by dragging are selected.