lexical syntax

In general, everything is space separated; there are no commas, semicolons, etc., in the syntax.

Comments are in the usual shell-ish style.

User names and repo names are as simple as possible; they must start with an alphanumeric, but after that they can also contain ., _, or -.

Usernames can optionally be followed by an @ and a domainname containing at least one . (this allows you to use an email address as someone's username). Reponames can contain / characters (this allows you to put your repos in a tree-structure for convenience)

continuation lines

There are no continuation lines -- gitolite does not process C-style backslash-escaped newlines as anything special. However, the section on "groups" will tell you how you can break up large lists of names in a group definition into multiple lines.

include files

Gitolite allows you to break up the configuration into multiple files and include them in the main file for convenience.

include     "foo.conf"

will include the contents of the file "foo.conf".

Details:

You can also use a glob (include "*.conf"), or put your include files into subdirectories of "conf" (include "foo/bar.conf"), or both (include "repos/*.conf").
Included files are always searched from the gitolite-admin repo's "conf/" directory, unless you supplied an absolute path. (Note: in the interests of cloning the admin-repo sanely you should avoid absolute paths!)
If you ended up recursing, files that have been already processed once are skipped, with a warning.

Advanced users: subconf, a command that is very closely related to include, is documented here.