From the ircg_eval_ecmascript_params source file:
   /*
    * State 0: Looking for ' or digit
    * State 1: Assembling parameter inside '..'
    * State 2: After escape sign: Copies single char verbatim, go to 1
    * State 3: Assembling numeric para, no quotation
    * State 4: Looking for ",", skipping whitespace
    */