[Zope] Variablizing size parameter

[Jay, Dylan]

I want to variablize the size parameter as I have done below 

<TR>
  <TD VALIGN="TOP">
  <STRONG><!--#var fieldName--></STRONG>
  </TD>
  <TD VALIGN="TOP">
  <i><!--#if "_.has_key(fieldID)"--><!--#var "_[fieldID]" size=fieldSize
etc="..."--><!--#/if--></i>
  </TD>
</TR>

It seems however that I get the error "a size attribute was used in a var
tag with a non-integer value.". So it appears to me that this can't be done.
Is that so?