Data is the object passed to the optgroup rendering method.
And so, you can put anything in it.
$('#selectize').selectize({
...
optgroupField: 'mygroup',
render: {
optgroup_header: function(data, escape) {
return '<div class="optgroup-header">' + escape(data.a) + escape(data.b) '</div>';
}
},
...
});
And then, whenever you want, you can add groups and options in the selectize:
//add group
var optGroup = { a: 'fruit', b: ... };
$('#selectize')[0].selectize.addOptionGroup('0', optGroup);
//add option
var option = { value: 'abc', text: 'banana', mygroup: '1'};
$('#selectize')[0].selectize.addOption(option);
Of course, if you only want a label for the group, you can do this:
//code
...
render: {
optgroup_header: function(data, escape) {
return '<div class="optgroup-header">' + escape(data) + '</div>';
}
...
//code
$('#selectize')[0].selectize.addOptionGroup('1', 'meat');
You can see the API demo (search for 'Optgroups (programmatic)' in page).