Add a placeholder to the Box Macro

Current :

Inserting a descendant of Box Macro (Info, Success, Warning, Error) with the WYSIWYG editor is adding an informal text as default content of the macro.
Info : Type your information message here.
Warning  : Type your warning message here.
Error : Type your error message here.
Success : Type your success message here.

Then the message have to be removed by the user when typing. This behavior is received as an inconvenience.

Expected :

From user point of view, the text is perceived as an input placeholder and should act like it, with an empty input that is directly editable.