Therefore, library should be able to order the parts to handle preference and be sure that HTML is preferred part for example even if multi-content is declared in another order.
Maybe this feature is not really useful because developer can have total control of order directly when he is using MultiTemplateContent ? Maybe the library should do it to avoid developers to know and handle this rule ?
Parts in a multipart MIME message should be in order of increasing preference. See http://www.w3.org/Protocols/rfc1341/7_2_Multipart.html section 7.2.3
Therefore, library should be able to order the parts to handle preference and be sure that HTML is preferred part for example even if multi-content is declared in another order.
Maybe this feature is not really useful because developer can have total control of order directly when he is using MultiTemplateContent ? Maybe the library should do it to avoid developers to know and handle this rule ?