The MIMP_MIME_Viewer_alternative class renders out messages multipart/alternative content types.
The MIMP_MIME_Viewer_html class renders out text/html MIME parts for MIMP, stripping the HTML so that the text can be safely converted to WML/CHTML/whatever is needed.
The MIMP_MIME_Viewer_multipart class handles multipart messages not rendered by any specific MIME_Viewer.
The MIMP_MIME_Viewer_plain class renders out text/plain MIME parts.
The MIMP_MIME_Viewer_related class handles multipart/related messages as defined by RFC 2112.
The MIMP_MIME_Viewer_status class handles multipart/report messages that refer to mail system administrative messages (RFC 3464).