How to get model's field name in custom editor template

I'm building my first custom editor template for a text area control. My code so far is -

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<dynamic>" %>
<%= Html.TextAreaFor( Model => Model , 2, 30, 
     new { @class = "html", @placeholder = ViewData.ModelMetadata.Watermark }) %>

It's not much so far, but it does work. But we need to add a character counter field to show remaining number of characters that the user can type in. I know how to do all the JavaScript to make this work.

So to keep naming system same, I'm going to add a control named ".charCounter" to display number of remaining characters left. My problem is that I cannot figure out the correct syntax to be able to retrieve the field name for the model.

The final version will look something like (JavaScript omitted) -

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<dynamic>" %>
<%= Html.TextAreaFor( Model => Model , 2, 30, 
     new { @class = "html", @placeholder = ViewData.ModelMetadata.Watermark }) %>
<span class="xxx">Remaining characters - 
     <input readonly type="text" name="<fieldName>.charCounter" />
</span>