Server Macro eXtensions, later re-christened Site Magic eXtensions, in a blatant fit of last ditch marketing. Product of The Internet Factory, (which, to my knowledge, is now defunct.) Interpreted originally under the CBuilder server software, now a module for IIS is also available.
Putting programmable elements interspersed in HTML is, of course a good idea, but, unfortunately for SMX, ASP and PHP do a much better job of it.
SMX's chief problem (IMHO, but I'm one of few people who are fluent in it, so it's an informed opinion) is that it doesn't line break well. e.g.:
do I write:
%foo('%bar('%baz(%quux%,%quuux%)))
or
%foo('%bar('%baz(%quux%,
%quuux%
)
)
)
or
%foo(
'%bar(
'%baz(
%quux%,
%quuux%
)
)
)
or perhaps
%foo(
'%bar(
'%baz(
%quux%
,
%quuux%
)
)
)
None of those is entirely satisfactory, and the most reasonable style differs from macro to macro.
%if() lines up well one way, whereas
%sql() lines up better another way, and %set() fits fine on a line by itself.