Kidogg wrote:

> Essentially an email template can contain any valid XHTML, but also has
> tags such as <membershipcardheader> and <membershipcardfooter> that can
> appear anywhere in the body of the HTML.

HTML email is an abomination, XHTML doubly so.

Although the "XHTML route" to adding these elements is obvious (look at
modularized XHTML) you're heading further and further away from what's
a realistically usable version of HTML for today's clients. I'd
strongly recommend that you stick with HTML 4.01 as any "public" use of
"HTML".

There's also a serious question as to why you need to include new tags
in publically published content. If they're new and unknown, then
what's the client expected to do with them ?  If they're unusable, why
include them ?

Assuming that they're significant for your in-house CMS, then I'd be
strongly inclined to use them internally with namespaced XHTML
(probably just XHTML 1.0 Strict), then strip them out with a final
"transcode for publication" step, possibly in XSLT, that also converts
it to HTML 4.01.  This is also a usable route to plaintext email.

PS - send HTML email to me and it goes straight into /dev/null/  You
_are_ going to support plaintext, aren't you?