Proportional measures of colwidth

The  docbook-xsl-1.61.2 fo stylesheet generates  output: 
<fo:table-column column-number="2"
                  column-width="proportional-column-width()" /> 
with a missing parameter  for  proportional-column-width()
for column widths give proportionally if "*" is written instead of "1*"

for example:  
<informaltable>
     <tgroup cols="3"  rowsep="0" >
      <colspec align="left" colsep="0" colwidth="3*" />
      <colspec align="center" colsep="0" colwidth="*"/>
        <colspec align="left" colsep="0" colwidth="3*"/>
    <tbody>
     ...

  Ian Moor
Ian W Moor                   Department of Computing,
           Imperial College.
                                   180 Queensgate
                                     London SW7 2AZ UK.