I have no idea when Apache first supported SSI , but personally I never knew it existed until years after PHP became popular.
I would guess , assuming that `Options +Includes` cannot be done by unprincipled users, that this being a disabled-by-default feature it was inaccessible to majority of us.
My shared hosting from claranet supported ssi via a .htaccess configuration.
Technically php was around at that point, but I don’t think it became popular until php3 - certainly my hosting provider didn’t support it until then.
"src/modules/standard/mod_include.c" says:
/*
* http_include.c: Handles the server-parsed HTML documents
*
* Original by Rob McCool; substantial fixups by David Robinson;
* incorporated into the Apache module framework by rst.
*
*/
Rob McCool is the author of NCSA HTTPd so it seems there is direct lineage wrt. this feature between the two server implementations.> You either copied and pasted your header into every single HTML file (and god help you if you needed to change it), or you used <iframe> to embed shared elements. Neither option was great.