To allow an .shtml file to parse a .php include:

<code>
<Directory "/path/to/directory/">
    Options FollowSymLinks Includes Indexes
    IndexOptions +NameWidth=*
</Directory>
</code>

Then in the .shtml file use something like this:
<code>
<!--#include virtual="/directory/footer.php" -->
</code>

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To allow a .php file to include .shtml files, you may need to edit /etc/php.ini with the following changes:
<code>
include_path = /path/to/docs
doc_root = /path/to/docs
</code>
service httpd restart

And use the following type of syntax in the .php file:
<code>
<?php include("../templates/footer.shtml"); ?>
</code>
Note the leading “../” in the include path.
The include file does not have to be .shtml (could be .html or .php, obviously)