Comment 3 for bug 499742

Ok, I started with a .vm file containing just the following lines:

(setq vm-mime-internal-content-type-exceptions '("text/html"))
(add-to-list 'vm-mime-type-converter-alist
      '("text/html" "text/plain"
        "lynx -force_html -dump -pseudo_inlines -stdin"))
(setq vm-mime-show-alternatives t)

Both text/plain and text/html were displayed. Is this what you get?

This behaviour seems reasonable because show-alternatives is true. So, both the alternatives are displayed.

In my normal use, I don't use a converter for text/html. So, I get a button displayed for it, and I can click it to send the content to a web browser.

vm-mime-alternative-select-method doesn't seem to have any effect once you have show-alternatives set to t. If you set it to nil, then the 'best method chooses text/html and lynx, 'best-internal chooses text/plain. The 'mixed method is displaying both, but I never knew what 'mixed is for. There is no documentation on it.
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I am beginning to understand what you are after. You want the alternative-select-method to continue its effect even if show-alternatives is set to t. You want the unselected alternatives to be displayed as buttons. Am I right?

Uday