If the <em>Source</em> button is available in the toolbar, users can click this button to disable the visual editor and edit the HTML source directly. After toggling back, the visual editor uses the allowed HTML tags to format the text — independent of whether buttons for these tags are available in the toolbar. If the text format is set to <em>limit the use of HTML tags</em>, then all excluded tags will be stripped out of the HTML source when the user toggles back to the text editor.