CSS rules with multiple possible values (jQuery)

The question is simple; using jQuery's css function, the computed style of a CSS attribute may be returned, but what if there are more than one style for that attribute being rendered? For example :

<div id="foo" style="text-decoration:underline;">Some underline text</div>

The instruction $('#foo').css('text-decoration'); will return underline. Now if I change it to

<div id="foo" style="text-decoration:underline;">Some underline <span id="bar" style="text-decoration:line-through;">text</span></div>

The instruction $('#bar').css('text-decoration'); will return line-through, alright.

But the actual text is also underline! How can I return both? Do I need to search all ancestors if I want to know if some text is both underline and line-through? Sounds a bit painful, no?

** Edit **

Another problem arises whith this HTML

<span style="text-decoration:underline;">some <span id="e1" style="font-weight:bold;">text</span></span>

where $('#e1').css('text-decoration'); returns none for some reason, while the text is clearly rendered with an underline.

** Disclaimer **

This question is not to debate how the UA renders an element, but if an element hierarchy applies a CSS or not. If one wants to understand text-decoration better, I suggest one would read about it. The question tries to focus on a more generalize matter. For example, it can also apply to this HTML

<div style="display:none;">Some <span id="keyword" style="text-decoration:underline;">hidden</span> text</div>

where one could want to know if the element keyword is visible or not. With the code below, this is simply done with

cssLookup($('#keyword'), 'display', 'none');   // -> true

** UPDATE **

After all the answers and comments, here is, based on Brock Adams solution :

/**
 * Lookup the given node and node's parents for the given style value. Returns boolean
 *
 * @param e     element (jQuery object)
 * @param style the style name
 * @param value the value to look for
 * @return boolean
 */  
function cssLookup(e, style, value) {
    var result = (e.css(style) == value);
    if (!result) {
        e.parents().each(function() {
            if ($(this).css(style) == value) {
                result = true;
                return false;
            }
        });
    }

    return result;
}

Thank you, everyone, for your inputs.