/// <summary>
/// Add method to make it accessible at runtime while creating custom validation at runtime.
/// Also add a method with same name to the CustomValidator.cs file to make it available for validation at server side.
/// </summary>

function ValidateHtmlEditorForRequired(sender, args) {
    if (ExtractContentFromHtmlContent(args.Value).trim().length < 1)
        args.IsValid = false;
    else
        args.IsValid = true;
}