>>> Hopefully the simpler solution which uses the existing value of
>>> `org-babel-current-src-block-location' will prove sufficient (once
>>> someone implements it that is...).
>>
>> I'll implement it and see if this seems more useful than the current
>> behaviour.  If it is, then we'll have to decide if that new behaviour
>> replaces the old one or yet another header argument or option switches
>> between old and new.  I guess it could be arranged so that the old-style
>> properties kept the old behaviour and the new-style properties followed
>> the new…
>
> I've pushed this to master, with documentation and testing.  Old style
> property-based header arguments keep the old behaviour of looking up the
> properties at the point of source block definition for backwards
> compatibility and are now deprecated.  The new header-args[:lang]
> properties use the location of the call as recorded in
> `org-babel-current-src-block-location'.
>

This is great, thanks.  I now see that we had different things in mind
when talking about the location used when evaluating header arguments,
however both were required and are now implemented.

You implemented location-specific look up of header argument properties,
I just pushed up location-specific evaluation of elisp embedded in
header arguments as shown in the attached example file.

Thanks,