syntax for passing attribute value to simple acl function

I'm having trouble figuring out how to pass an attribute value to a simple acl function that formats and returns the value to save it to a variable. The attribute is "revdate" and the eic is "cmm"

<e-I-c gi="cmm>

...

<att>

<specval attname="revdate" attval="#ANY">

<fillval attname="myfuncs::format_date" attloc="system-func" fillcat="savetext" fillchar="conrule">

<charsubset>

<savetext textid="issuedate.txt">

</charsubset>

Plus I know I'm not declaring the function correctly:

function format_date(window,oid)

...

local date=oid_attr(oid, ?);

...

Any help is appreciated.