Parse attributes from MvcHtmlString
===

I need to be able to parse the attributes from an MvcHtmlString (the results of an HtmlHelper extension), so that I can update and add to them.

For example, take this HTML element:

    <input type="text" id="Name" name="Name" 
     data-val-required="First name is required.|Please provide a first name.">

I need to take the value from `data-val-required`, split it into two attributes with the second value going into a new attribute:

    <input type="text" id="Name" name="Name" 
     data-val-required="First name is required."
     data-val-required-summary="Please provide a first name.">

I'm trying to do this with an HtmlHelper extension method, but I'm not sure the best way to parse the attributes.