bool _isMultipart(int &$mid, str $subtype)

Searches a message's structure to see if a multipart/$subtype MIME type appears, where $subtype is one of related or mixed. This is done by calling on Mail_IMAPv2::extractMIME internally. If the multipart/related MIME type appears in a message's parsed structure, Mail_IMAPv2::_scanMultipart uses the presence of that MIME type to adjust to anomolies in the message's stucture.

Warning: For most messages, the multipart/related MIME type does not appear in the parsed structure of the message. Therefore, Mail_IMAPv2::_isMultipart should not be used to determine whether a message is a multipart/related message. The Mail_IMAPv2::getRelatedParts method is provided to determine whether a message has related parts.

Warning: As a method used internally by Mail_IMAPv2, Mail_IMAPv2::_isMultipart should not be used directly. Its API has the potential of being changed in future releases, should I find a more efficient approach.