Well, I am STOKED.
Don't know how I blundered across it, but turns out Apache has an SSI Tutorial
[httpd.apache.org]. And by some weird oversight it's written in perfectly intelligible English.
So with the aid of MAMP I tried it and it works! Woo hoo! No more having to edit every single document when I change a directory somewhere. Only one 500 error along the way-- and it came from MAMP, not the live site. (Funny to have your own computer spitting 500 errors at you.) And one blunder in url formatting. Fortunately only Yandex saw it, and they're much quicker on the uptake than g### so I won't be flooded with 404s for the next three years.
One quibble: It would have been amazingly, fantastically, superbly useful and helpful and all-around beneficial if the tutorial had dropped just a teeny tiny little inkling of an allusion to an iota of a hint that the line
chmod +x pagename.html
DOES NOT GO IN THE HTACCESS. Ahem. See above about 500 error.
Matter of fact, the line doesn't go anywhere ;) On my local computer, "chmod +x " goes in Terminal, followed by dragging up the relevant file's icon so I don't have to type its name and get the slashes and paths wrong. On the real site, it's done by clicking a box in Fetch after poring over the Help to find out why the box has suddenly disappeared, followed by trial and error to see which of three identical boxes gets checked
Right now it's a compromise. The main htaccess says
Options -Indexes +Includes
SSIErrorMsg "<!-- SSI error -->"
(Includes are probably on by default, but let's not take any chances. And the next passing human doesn't need to see the default "This page was coded by someone who doesn't know how to make SSIs work correctly".)
Five directories have matching htaccess files that say
AddType text/html .html
AddOutputFilter INCLUDES .html
One directory has an htaccess that says
accompanied by a cluster of manually set permissions. (It had to be handled differently because this directory includes a zillion html files that won't
be using any Includes. At least not yet. 2 or 3 other top-level directories don't use Includes at all-- and probably never will.)
And my hard drive is littered with .htaccess files. Could have put the information straight into MAMP's config file, but it made more sense to match the arrangement of the "live" site. The computer itself won't let me name files with leading dot, but the text editor will if I click an extra box saying "Yes! I really mean it!" Neener-neener.
The one place I'm not using includes is the one you'd think is the most obvious candidate: the "last edited..." footers. I don't want them to change each time I open the page to fix a link or fine-tune something in the formatting. Only when I've made a substantive change to page content. And then of course I've already got the page open anyway.
One of these years I'll venture into simple programming, so all directories can use the same Include file with the aid of some variable or other. But today I'm resting.
Just thought I'd share. :)
Now sitting back waiting for g1 or someone like him to stop by and scream Nooo! You can't do it that way! You're insane! Your server will explode!