+ * * Pass a base64-encoded SVG using a data URI, which will be colored to match the color scheme.
+ * This should begin with 'data:image/svg+xml;base64,'.
+ * * Pass the name of a Dashicons helper class to use a font icon, e.g. 'dashicons-piechart'.
+ * * Pass 'none' to leave div.wp-menu-image empty so an icon can be added via CSS.