At the top of the message console, there are checkboxes for the various message severities (Error, Critical Warning, Warning, Info, Status).
De-selecting the checkbox will filter out messages for that severity so that they are not displayed in the message window.
If the width of the message console is not wide enough to display all of the severities, a ">>" icon is placed at the top right of the window.
If I click on the ">>" icon, the missing severities are displayed in a pop-up window.
However, I am not able to select or deselect these message severities.
In order to select or de-select a message severity, it has to be clicked on from the main message console window.
To do this, the window width might need to be expanded to select the desired severity of messages you would like to display.