Stale Message Safeguard

I don't really have a clear idea how you'd best design it, but some form of support for expiring message values after a defined time. For example: using pAcommsHandler, as is, the latest nav_x,nav_y pair would be taken from MOOS and tx'ed using goby. But that pair could have any age: it wouldn't be useful to send these values if they are, say, 2mins old. (I guess we kind of assume that these values are regularly produced at high frequency at present)

I imagine that this could be an extra field in the xml description:
      <float>
        <name>nav_x</name>
        <moos_var>NAV_X</moos_var>
        <max>100000</max>
        <min>-100000</min>
        <precision>1</precision>
        <expire>20</expire> ... where 20 is the number of seconds before that value expires
      </float>

I assume that you'd need a special value of the nav_x variable to indicate this value has expired or the message would not be created if any of the values are outside their expiration period.