[Zpt] XHTML validation and <span>

[Tim Peters]

>>   <title tal:insert="string: The title is: ${python:5*10}">object
>>   title</title>

[Todd Coram]
> Oooh. Sick. This would be very cool (where are the language lawyers? Tim?
> Guido?).

It's a Universal Law:  every little language swells until you can implement
an email client in it.  You can restrict it at the start, but over the years
it won't last.  So do what you want here, provided only that we don't make it
*impossible* to extend later.  Nested braces aren't a problem, provided that
it remains possible to distinguish braces intended for the "python:" (in
general, "xyz:") processor from those intended to delimit the text passed to
it; e.g., this could cause a problem:

    "string: The title is: ${python: len('}')}"

In general, TAL can't know the internal rules for "python:" expressions,
right?  Then to be completely general, TAL must recognize some escape
sequence to allow passing "its own" characters into the xyz: processor; like

    "string: The title is: ${xyz: len('\}')}"

I'm not saying we should do this; I'm saying it would be a Very Bad Idea to
do anything now that would *prevent* us from doing this later.

the-more-successful-a-language-the-more-pressure-to-extend-it-so-
    don't-plan-for-failure-ly y'rs  - tim