Conditional attribute rendering

default boolean behavior

@using System.Collections.Generic
@{
    ViewData["Title"] = "Home Page";
    var Colors = new List<string>
    {
        "thunderbird",
        "mandarin",
        "saffron",
        "shamrock",
        "aqua",
        "royal",
        "lavender"
    };
    var selectedColor = "aqua";
}
@foreach (var color in Colors)
{
    @color <input type="radio" id="@color" value="@color" checked="@(color == selectedColor)" /><br/>
}
        
output:

thunderbird <input id="thunderbird" type="radio" value="thunderbird"><br>
mandarin <input id="mandarin" type="radio" value="mandarin"><br>
saffron <input id="saffron" type="radio" value="saffron"><br>
shamrock <input id="shamrock" type="radio" value="shamrock"><br>
aqua <input id="aqua" type="radio" checked="checked" value="aqua"><br>
royal <input id="royal" type="radio" value="royal"><br>

https://weblogs.asp.net/jongalloway/asp-net-4-beta-released

Conditional attribute rendering
If you have an attribute that might be null, in the past you've needed to do a null check to avoid writing out an empty attribute, like this:

<div @{if (myClass != null) { <text>class="@myClass"</text> } }>Content</div>
Now Razor is able to handle that automatically, so you can just write out the attribute. If it's null, the attribute isn't written:

<div class="@myClass">Content</div>
So if @myClass is null, the output is just this:

<div>Content</div>
Again, this is a Razor feature, so it's shared with ASP.NET Web Pages 2.
lavender <input id="lavender" type="radio" value="lavender"><br>