What is $.label.text in titanium alloy application?

Hi all

I am learning titanium alloy for past couple of hours, when I created a titanium alloy project it has by default created me a hello world application.

index.xml

<Alloy>
    <Window class="container">
        <Label id="label" onClick="doClick">Hello, World</Label>
    </Window>
</Alloy>

// index.js

function doClick(e) {
    alert($.label.text);
}
 
$.index.open();

Here my question is ** what is $.label? ** is $. is used here to refer a tag's id attribute's value ? Could some one please help me in understanding this ?

Thanks

Varun Krishna. P