The View Markup command has a submenu with options to control markup in the Authentic XML document. With the four markup commands (screenshot below), you can select between the Hide Markup and the various Show Markup modes.
The markup refers to how the various node tags are displayed in Authentic View. These are mutually exclusive options, and one option must be selected at any given time. With Hide Markup selected node tags are not displayed. Small Markup shows opening and closing tags without node names. Large Markup shows opening and closing node tags with their respective node names. Mixed Markup refers to the markup specified in the Authentic Node Properties of individual nodes. Since the default markup property for individual nodes is Hide Markup, no markup (either small or large) will be displayed—unless you have specified (as a node property) small or large markup for some node/s.