* @param helpTopic the help topic this button will open when clicked, <code>null</code> to open the base documentation URL
*/
public HelpButton(MainFrame mainFrame, String helpTopic) {
Map<String, Object> properties = new Hashtable<String, Object>();
GoToDocumentationAction action = new GoToDocumentationAction(mainFrame, properties);
setAction(action);
if(helpTopic!=null)
setHelpTopic(helpTopic);
// Note: the button's text and icon must be set after the action otherwise they'll be replaced by the action's
// Remove the action's label from this button's text
setText(null);
// Use the action's label as a tooltip
setToolTipText(action.getLabel());
if(OsFamily.MAC_OS_X.isCurrent() && OsVersion.MAC_OS_X_10_5.isCurrentOrHigher()) {
// If running Mac OS X 10.5 (and up), use the special client property to have a standard help button.
putClientProperty("JButton.buttonType", "help");