I have a set of custom ASP.NET server controls, most of which derive from CompositeControl. I want to implement a uniform look for "required" fields across all control types by wrapping each control in a specific piece of HTML/CSS markup. For example:

  <div class="requiredInputContainer">
        ...custom control markup...
  </div>

I'd love to abstract this behavior in such a way as to avoid having to do something ugly like this in every custom control, present and future:

  public class MyServerControl : TextBox, IRequirableField { 

          public IRequirableField.IsRequired {get;set;}

          protected override void Render(HtmlTextWriter writer){

            RequiredFieldHelper.RenderBeginTag(this, writer)
            //render custom control markup
            RequiredFieldHelper.RenderEndTag(this, writer)
          }
   }

  public static class RequiredFieldHelper{

      public static void RenderBeginTag(IRequirableField field, HtmlTextWriter writer){
      //check field.IsRequired, render based on its values
      }
      public static void RenderEndTag(IRequirableField field, HtmlTextWriter writer){
       //check field.IsRequired , render based on its values
      }

  }

If I was deriving all of my custom controls from the same base class, I could conceivably use Template Method to enforce the before/after behavior;but I have several base classes and I'd rather not end up with really a convoluted class hierarchy anyway.

It feels like I should be able to design something more elegant (i.e. adheres to DRY and OCP) by leveraging the functional aspects of C#, but I'm drawing a blank.