The IStringList::get__NewEnum method retrieves an enumerator interface which can be used to iterate through the items in the string list.
HRESULT get__NewEnum(
IUnknown ** ppEnumReturn // pointer to an IUnknown interface
// pointer that receives the enumerator
);
The Form, QueryString, and ServerVariables collections return parameter values as an array. You can use this method to retrieve an enumerator to iterate through one of the string list collections.
QueryString, Form, ServerVariables