What is the meaning of the icon that can be changed in text messages reading pane

[AC Question]

when reeding a text from a friend who also has and HTC , the Text icon in the top of the reading pane, next to the contact name can be changed from a standard text box to a text box with a smaller box in the background by clicking on it. This icon placed next to the 3 line options tab . Can anyone tell me what this means / does ?

 

[B. Diddy]

Welcome to Android Central! Can you show us a screenshot? http://forums.androidcentral.com/am...ide-how-post-screenshots-android-central.html