I think that a flag may not even be necessary -- the TT syntax won't conflict with the current letter formats, and is unlikely to be entered accidentally. I think that we could simply silently start to support TT, and no one would be the wiser, except for those who want to use it.

This also addresses Heather's concern -- the initial transition would be essentially un-noticable. 

On Wed, Feb 3, 2016 at 10:22 AM, Galen Charlton <gmc@esilibrary.com> wrote:
Hi,

On Wed, Feb 3, 2016 at 8:56 AM, Kyle Hall <kyle.m.hall@gmail.com> wrote:
> I think Jonathan has an excellent plan of attack, but it does require a
> complete switchover all at once.

Rather than forcing a complete switchover right off the bat, I suggest
adding a flag that specifies whether old-style or TT templates are in
effect for a given notice.  That way, we'll have much more flexibility
to design the new templating mechanism to take full advantage of
Template Toolkit, and folks will have the ability to migrate their
notices definitions on their own schedule.

Regards,

Galen
--
Galen Charlton
Infrastructure and Added Services Manager
Equinox Software, Inc. / The Open Source Experts
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