[Zope] mid function

I checked through the DTML function i could not find this function. I am writing a code where i will need to store the title of each dtml document with <dtml-let > and extract certain number of xters from the title and test it before calling a particular object. This function is widely used, but this is the way is been used in Vb mid(string, start [,length]) string - denote the var name start - " where you want to begin the extraction length - " the no of xters you want extract from the string E.g. let say my title is sunday05082001 then if i specify mid(title, 1, 6) the result of the fuction will be sunday. kindly help me out.