Improve this Doc

# Error: $compile:tplrt
Invalid Template Root

    Template for directive '{0}' must have exactly one root element. {1}

## Description

When a directive is declared with `template` (or `templateUrl`) and `replace` mode on, the template must have exactly one root element. That is, the text of the template property or the content referenced by the templateUrl must be contained within a single html element. For example, `<p>blah <em>blah</em> blah</p>` instead of simply `blah <em>blah</em> blah`. Otherwise, the replacement operation would result in a single element (the directive) being replaced with multiple elements or nodes, which is unsupported and not commonly needed in practice.

For example a directive with definition:

    myModule.directive('myDirective', function factory() {
      return {
        ...
        replace: true,
        templateUrl: 'someUrl'
        ...
      }
    });

And a template provided at URL `someUrl`. The template must be an html fragment that has only a single root element, like the `div` element in this template:

    <div><b>Hello</b> World!</div>

An an invalid template to be used with this directive is one that defines multiple root nodes or elements. For example:

    <b>Hello</b> World!

Watch out for html comments at the beginning or end of templates, as these can cause this error as well. Consider the following template:

    <div class='container'>
      <div class='wrapper>
         ...
      </div> <!-- wrapper -->
    </div> <!-- container -->

The `<!-- container -->` comment is interpreted as a second root element and causes the template to be invalid.