How to export all elements in a iPhone WhatsApp chat?
CopyTrans Contacts is an application which can export WhatsApp chats in several formats, including HTML pages and Word documents with intenal links to attachments; this allows easy and comfortable reviewing of the exported chats.

CopyTrans Contacts is not free, but a limited trial is available; the trial allows up to 50 actions to be performed, and a full export of a WhatsApp chat counts as a single action; therefore, the trial version is more than enough for exporting the full contents of one or more chats.