[Petal] local defines

[Fergal Daly]

How closely is Petal supposed to match TAL? It seems there is no way to have a 
local define. This doc

<doc>
  <outer petal:define="var string:a">
    <inner petal:define="var string:b">
      <tag petal:content="var" />
    </innner>
    <tag petal:content="var" />
  </outer>
</doc>

gives output of

<doc>
        <tag>
                <tag>
                        <tag>b</tag>
                </tag>
                <tag>b</tag>
        </tag>
</doc>

but the defines weren't global defines, so when we leave the "inner" tag, the 
value of var is supposed to go back to "a". I tried putting define="local var 
string:b" but I got an error. Is it possible to have locally scoped 
variables? Can PIs support this?

Fergal