function set_class_if_present(div_id, class_name)
{
 if(document.getElementById(div_id) != undefined)
 document.getElementById(div_id).className = class_name;
}

function get_class_if_present(div_id)
{
 if(document.getElementById(div_id) != undefined)
 return document.getElementById(div_id).className;
}
function set_tab_off(tab_id)
{
 set_class_if_present(tab_id, 'off');
 }

function show_tab(div_id) {
	hide_if_present('howtobuy');
	hide_if_present('longdescription');
	hide_if_present('support');
	hide_if_present('FAQ');
	hide_if_present('videos');
	hide_if_present('specification');

	set_tab_off('howtobuy-tab');
	set_tab_off('longdescription-tab');
	set_tab_off('support-tab');
	set_tab_off('FAQ-tab');
	set_tab_off('videos-tab');
	set_tab_off('specification-tab');

document.getElementById(div_id).style.display = 'block';
document.getElementById(div_id + '-tab').className = 'on';
}

function hide_if_present(div_id)
{ 
if(document.getElementById(div_id) != undefined)
document.getElementById(div_id).style.display = 'none';
}