tags is included from html files. The code for this include
<xt:include file="/manual/files/included" />
From html you can also declare a default file to be included if the file does not exist
<xt:include default="/manual/files/default" file="/manual/files/no_such_file" />
This is the default include file. You can also do a random include of text or html files, Again Only the content between the tags is included from html files
<xt:include file="/manual/files/random/*" />