What does these symbols represent? (bottom right of the window)

[Mikeyws]

At the bottom right of the window, there is this symbol: . When it is pressed is changes to anther symbol and again to another before looping back to the original symbol. What does these symbols represent? 

[RandallCrandall'sCandleHandle · Accepted solution]

Hey Mikeyws,

This changes the text selection mode for editing.

Cheers,

Ryan C.