 
   func expand(# value:String) -> String {
     return value
+  }
+
+  func expand(# value:String, prefix:Int?) -> String {
+    if let prefix = prefix {
+      if countElements(value) > prefix {
+        let index = advance(value.startIndex, prefix)
+        return expand(value: value.substringToIndex(index))
+      }
+    }
+
+    return expand(value: value)
   }
 }
 


  override func expand(variable:String, value:AnyObject?, explode:Bool, prefix:Int?) -> String {
    if let value:AnyObject = value {
      return "\(variable)=\(value)"
    }

    return ""

    if let value:AnyObject = value {
      let value = "\(value)"
      if countElements(value) > 0 {
        let expandedValue = expand(value:value, prefix:prefix)
        return "\(variable)=\(expandedValue)"
      }
    }

