How does jQuery's val(value) set the selected value in a dropdownbox (underwater)

I am working with ASP.NET MVC 3 and jQuery 1.5.

Somewhere in my code I use jQuery to set the selected value of a dropdownbox like so:

$("#SelectedFilterOption").val(filter开发者_开发百科Option)

filterOption is the value of the option field, not the text. On my screen I see the right value as selected, however, when I look at the html, I do not see any option element with the selected attribute set. When I post these values to to my ASP.NET MVC 3 app, how do "they" know what value is selected?

Edit:

$("#SelectedFilterOption").val() does return the right value. Also I noticed that when I set the initial selected value from ASP.NET MVC, that element will get the selected attribute. The selecte dattribute stays on the field in the html, even when I manually select another option.

I will inspect this with firebug as well (in addition to chrome and IE9 tools).

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It finds the index of the first item with that value.

When it has the index, it uses <select>'s .selectedIndex=targetIndexNumber property via DOM. Editing the html is not required. Some browsers do that themselves, others don't bother.