This character is the classical ASCII LF, code=10. 2- The effect is achieved in Calc by inserting an actual character into the text. 1- To enter a line feed (hard line break) while editing the text content of a cell in Calc Ctrl+Enter must be pressed (On Mac: Cmd+Enter). As this thread got nearly 50 000 views to date (which means a very high rank), and the situation has changed since the original question was posted, I would lik to give a compendium of the current state (as of, AOO V 4.1.3):
