jQuery extend of jQuery UI autocomplete - jquery-ui

Question

I am trying to extend the default jQuery UI 1.8.16 autocomplete plugin to do a few things:
Check an array of values and not just the label/value when searching for a match
Render the menu item in a different pattern based on a category on the item
So to do this I began to work through the code. I am very new to writing a widget/plugin and so I am wondering if someone can help me understand this part. I am currently trying to do the following:
$.widget("custom.advautocomplete", $.ui.autocomplete, {
filter: function (array, term) {
var matcher = new RegExp($.ui.autocomplete.escapeRegex(term), "i");
return $.grep(array, function (value) {
return matcher.test(value.label || value.alldata || value);
});
},
_renderMenu: function (ul, items) {
var self = this,
currentCat = "";
$.each(items, function (index, item) {
if (currentCat != item.category) {
ul.append("<li class='ui-autocomplete-category'>" + item.category + "</li>");
currentCat = item.category;
}
self._renderItem(ul, item);
});
},
_renderItem: function (ul, item) {
return $("<li></li>")
.data("item.autocomplete", item)
.append($("<a></a>").text(item.alldata))
.appendTo(ul);
}
});
The _renderMenu code is pretty much taken directly from the example in the documentation. The _renderItem code is working in this example as well. What is not working is the filter code. I did notice that the filter code is defined in the jQuery library like so:
$.extend($.ui.autocomplete, {
escapeRegex: function (value) {
return value.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&");
},
filter: function (array, term) {
var matcher = new RegExp($.ui.autocomplete.escapeRegex(term), "i");
return $.grep(array, function (value) {
return matcher.test(value.label || value.value || value);
});
}
});
From what I've gathered so far, this is extending the jQuery autocomplete which is defined earlier by a call to $.widget("ui.autocomplete"... But why is this handled this way? Why are these two functions not handled inside the widget definition like everything else? I noticed that if I extend ui.autocomplete in the same manner as it is done by the base widget, then I can get the filter override to work. I would like to extend the control and include the new filter at the same time so I can keep my code a bit cleaner but I don't understand why it is being done like this. Is there a benefit that I'm missing?