The most important part of this line is the "onclick" attribute. When this checkbox is clicked the 'races' argument tells gCalMarkup to change whether the Races calendar is shown or hidden. The "false" argument tells gCalMarkup not to change any other calendars. The calendarSelect "id" attribute must end with the name of the calendar and allows gCalMarkup to find the checkbox so it can be set or cleared. The calendarSelect "name" attribute must be as shown and is used to group all the checkboxes together as a group (used below to hide the other calendars). Lastly, the checked="checked" attribute indicates that this calendar should be shown when the page first loads.
The next line displays the "Races" link next to the checkbox. When this link is clicked, the Races calendar is shown and any other calendars are hidden:
The same "onclick" attribute is used in this link that was used in the checkbox above. The difference is the "true" argument which tells gCalMarkup to show the "Races" calendar and to hide all of the others (see the "name" attribute above).
The next two lines are the same as the first two, except they are for the "Club Events" calendar instead of for the "Races" calendar. Notice that the "name" parameter contains the same "calendarSelect" name:
Lastly, we add a calendar status line:
This line displays the "2 of 2 calendars loaded" line that indicates how many calendars there are and how many are currently displayed.