Examine the header of the first body part. Find the second boundary, terminating the first body part and initiating the second. The first child object is completed. Start off a sister object to the previous child object. Examine the header of the second body part.
End of data is reached, message parsing is completed.
We've got a hierarchical message structure describing the incoming message. Parse the message structure, converting the data. Thus, decode quoted-printable. Target format does not want Base64, decode Base64. Target format does not want binary, encode UUencode.