[Zope] Assigning strings using DTML-LET

I'm trying to assign the string: 1=1 to the variable criteria using this construct: <dtml-let criteria='1=1'> but I can't because Zope complains: invalid parameter: "=1'", for tag <dtml-let criteria='1=1'>, on line 5 of Create_List Some playing around reveals that it doesn't like spaces and the equals sign (=) in the string. Am I correct in thinking that something delimited by single quotes (eg. 'this is a string') is a string? If so why can't I (or how can I) include spaces and the equal sign inside the string. thanks - Jason Wong