Plugin within a Plugin

I wrote a plugin I want to wrap around the imgsizer plugin. I debugged my plugin and it works ok on its own but it doesn’t work when I put the imasizer plugin inside the tag…

{exp:dirdump dir='./nest/proj/images/facility'}
  {exp:imgsizer:size src="{file}" width="200"}
      {sized}
  {/exp:imgsizer:size}
{/exp:dirdump}

I suspect that when the $this->EE->TMPL->fetch_param() function in the plugin is confused by the imgsizer tag and does not see the {file} param hiding within. Is there a post or wiki that discusses this issue and how to deal with it? Do I have to parse the imgsizer tag on my ownI am going to look at some of the other modules that can do this and try and reverse engineer it.

E.E. version 2.1.1 Build: 20101020