Writing a text is a complex task that needs a coordinated implementation of a large set of mental activities. Writers have to clearly delimitate the nature, the goal and the communicative function of the text. They also have to establish a precise representation about reader" characteristics and expectations, in order to anticipate systematically what must, or can, be written. Writers have equally to control the text topic so as to generate or to specify the most relevant ideas that will progressively constitute the text content. In addition, they must sometimes clarify the message, reorganise, modify and articulate ideas, while controlling the whole text coherence.