Hello,

I would suggest you to take advantage of the Visible property of the Editable text webpart. You can see a basic example here: http://devnet.kentico.com/FAQs/Web-parts---Controls/How-to-show-hide-webpart-on-specific-document-with.aspx. Using this approach, the content before/after is shown just if the webpart has set visibility to the true value.

In your case, you can develop a custom macro which will check, whether the editable region has some content or not. It can look similar to the following code:

case "iseditableregionpopulated":
match = true;

result = "true";

if (CMS.CMSHelper.CMSContext.CurrentDocument.DocumentContent.EditableWebParts["maincontenttext"] != null) // if the editable region exists
{
    string contentText = CMS.CMSHelper.CMSContext.CurrentDocument.DocumentContent.EditableWebParts["maincontenttext"].ToString(); // get its content
    if (((contentText.Trim() == "") || (contentText.Trim() == "<br />")) && (CMS.CMSHelper.CMSContext.ViewMode == CMS.PortalEngine.ViewModeEnum.LiveSite)) //check whether it is empty and do that only on the live site
    {
        result = "false";
    }
}
else if (CMS.CMSHelper.CMSContext.ViewMode == CMS.PortalEngine.ViewModeEnum.LiveSite) // if editable region doesn't exist and you are on the live site - hide it
{
    return "false";
}
break;

You can call this macro like this: {% ProcessCustomMacro("iseditableregionpopulated", "") %}

Best regards
Ondrej Vasil