Initializes selectize from a <select> element.

@param {object} $input
@param {object} settings_element
function($input, settings_element) {
		var i, n, tagName, $children, order = 0;
		var options = settings_element.options;
		var optionsMap = {};

		var readData = function($el) {
			var data = attr_data && $el.attr(attr_data);
			if (typeof data === 'string' && data.length) {
				return JSON.parse(data);
			}
			return null;
		};

		var addOption = function($option, group) {
			$option = $($option);

			var value = hash_key($option.val());
			if (!value && !settings.allowEmptyOption) return;

			// if the option already exists, it's probably been
			// duplicated in another optgroup. in this case, push
			// the current group to the "optgroup" property on the
			// existing option so that it's rendered in both places.
			if (optionsMap.hasOwnProperty(value)) {
				if (group) {
					var arr = optionsMap[value][field_optgroup];
					if (!arr) {
						optionsMap[value][field_optgroup] = group;
					} else if (!$.isArray(arr)) {
						optionsMap[value][field_optgroup] = [arr, group];
					} else {
						arr.push(group);
					}
				}
				return;
			}

			var option             = readData($option) || {};
			option[field_label]    = option[field_label] || $option.text();
			option[field_value]    = option[field_value] || value;
			option[field_disabled] = option[field_disabled] || $option.prop('disabled');
			option[field_optgroup] = option[field_optgroup] || group;

			optionsMap[value] = option;
			options.push(option);

			if ($option.is(':selected')) {
				settings_element.items.push(value);
			}
		};

		var addGroup = function($optgroup) {
			var i, n, id, optgroup, $options;

			$optgroup = $($optgroup);
			id = $optgroup.attr('label');

			if (id) {
				optgroup = readData($optgroup) || {};
				optgroup[field_optgroup_label] = id;
				optgroup[field_optgroup_value] = id;
				optgroup[field_disabled] = $optgroup.prop('disabled');
				settings_element.optgroups.push(optgroup);
			}

			$options = $('option', $optgroup);
			for (i = 0, n = $options.length; i < n; i++) {
				addOption($options[i], id);
			}
		};

		settings_element.maxItems = $input.attr('multiple') ? null : 1;

		$children = $input.children();
		for (i = 0, n = $children.length; i < n; i++) {
			tagName = $children[i].tagName.toLowerCase();
			if (tagName === 'optgroup') {
				addGroup($children[i]);
			} else if (tagName === 'option') {
				addOption($children[i]);
			}
		}
	}