shows/hides markers on the page
Available only in PRO Edition
var marker1 = gantt.addMarker({ ...});
var marker2 = gantt.addMarker({ ...});
var marker3 = gantt.addMarker({ ...});
gantt.config.show_markers = false;// hides all 3 markers
This functionality is available in the PRO edition only.
This option is defined in the ext/dhtmlxgantt_marker.js extension, so you need to include it on the page. Read the details in the Adding Vertical Markers article.