Mixing C# and HTML Helper tags ASP.NET MVC 6 (ASP.NET Core)
<p>I'm using the new Helper tags in ASP.NET MVC 6.</p>

<pre><code>    &lt;form asp-area="DAS"
          asp-controller="Report"
          asp-action="Add"
          asp-route-id="@Model.id"
          asp-route-incBalance="@Model.incBalance"
          asp-route-dateSet="@Model.dataStart.ToString("yyyy-MM-dd")"
          asp-route-dateNext="@Model.dataEnd.ToString("yyyy-MM-dd")"
          method="post" role="form"&gt;
    &lt;/form&gt;
</code></pre>

<p>I want to routing attribute:</p>

<pre><code>asp-route-dateNext="@Model.dataEnd.ToString("yyyy-MM-dd")"
</code></pre>

<p>was applied only if:</p>

<pre><code>          {
              if (Model.incBalance == 0)
              {
                  asp-route-dateNext="@Model.dataEnd.ToString("yyyy-MM-dd")"
              }
          }
</code></pre>

<p>As a result, I want to get something like this:</p>

<pre><code>    &lt;form asp-area="DAS"
          asp-controller="Report"
          asp-action="Add"
          asp-route-id="@Model.id"
          asp-route-incBalance="@Model.incBalance"
          asp-route-dateSet="@Model.dataStart.ToString("yyyy-MM-dd")"
          {
             if (Model.incBalance == 0)
             {
                 asp-route-dateNext="@Model.dataEnd.ToString("yyyy-MM-dd")"
             }
          }
          method="post" role="form"&gt;
    &lt;/form&gt;
</code></pre>

<p>I get these errors:</p>

<blockquote>
  <p>TagHelper attributes must be well-formed.</p>

<pre><code>          if (Model.incBalance == 0)
</code></pre>
</blockquote>

<p>and</p>

<blockquote>
  <p>The tag helper 'form' must not have C# in the element's attribute
  declaration area.</p>

<pre><code>              asp-route-dateNext="@Model.dataEnd.ToString("yyyy-MM-dd")"
</code></pre>
</blockquote>

<p>I'm using Visual Studio 2015 Update 1</p>

<p><strong>Update 1:</strong>
I also tried this option:</p>

<pre><code>@(Model.incBalance == 0 ? "asp-route-dateNext=" + Model.dataEnd.ToString("yyyy-MM-dd") : string.Empty)
</code></pre>

<p>But the error remained:</p>

<blockquote>
  <p>The tag helper 'form' must not have C# in the element's attribute
  declaration area.</p>

<pre><code>      @(Model.incBalance == 0 ? "asp-route-dateNext=" + Model.dataEnd.ToString("yyyy-MM-dd") : string.Empty)
</code></pre>
</blockquote>