Example of Creating Custom Field in Task

Can somebody post an example of how to create a custom field. I have a task that runs, gets data from server, parses the data. I would like to assign part of the parse to a custom field name but have been unsuccessful in creating the custom field. Just putting it in the interface doesn't seem to do it. I have created an extends of the Task and added the field but I am not sure how to tell the Task an extend exists. I have something like the following:

<component name = "programContentReader" extends = "Task" >
  <interface>
  <field id = "content" type = "node" />
  <field id = "myfield" type = "string" />
  </interface>
  <script type = "text/brightscript" >
    <![CDATA[
    sub init()
      m.top.functionName = "readcontent"
    end sub

Function readcontent() as object
content = CreateObject("roSGNode", "ContentNode")
Stuff going on here to parse

dataItem = content.CreateChild("ContentNode")
dataitem.myfield= whatever is in parse
m.topcontent=content
end function

Extend of Task

<component name="extendprogram" extends="ContentNode" >
<interface>
    <field id ="myfield" type="string" />
   </interface>