Asks a movable's content to start editing: a text box puts the caret in its text.
Parameters
movable: IMovable
Returns boolean
true if the edit started now, false if it waits for the content.
Remarks
This is how a command reaches a content component it cannot see. A movable that is not drawn yet
— a note that only shows while selected or pointed at — starts editing when its content mounts,
as long as it is still selected then.
Asks a movable's content to start editing: a text box puts the caret in its text.