I’ve never bothered to do much research into a solution to a problem that I have had with SSI. I’ve been frustrated by the inability to use an SSI page for the common header information on a web site and still have page specific title and meta data. Then I ran across XSSI for Apache. It allows you to set variables within nested SSI documents. I.e., at the top of my index.shtml file is an SSI tag that declares the variable for the title of that page. Just below that tag is the SSI tag for the header document. The header document contains an SSI tag that populates the title based on what has already been set for the title variable in the index.shtml file.
Simple enough isn’t it.