the check-in, or it might be the name of a branch or tag, or it might
be a timestamp.  See the [./checkin_names.wiki|check-in name documentation]
for more possibilities and examples.  The <i>&lt;version&gt;</i> can
also be the special identifier "<b>ckout</b>".
The "<b>ckout</b>" keywords means to
pull the documentation file from the local source tree on disk, not
from the any check-in.  The "<b>ckout</b>" keyword
only works when you start your server using the 
"[/help?cmd=server|fossil server]" or "[/help?cmd=ui|fossil ui]"
commands.  The "/doc/ckout" URL is intended to show a preview of
the documentation you are currently but have not yet you checked in.

Finally, the <i>&lt;filename&gt;</i> element of the URL is the
pathname of the documentation file relative to the root of the source
tree.

<h1>2.0 Server-Side Text Substitution</h1>

Fossil can do a few types of substitution of server-side information
into the embedded document.

<h2>2.1 "$ROOT" In HTML and Markdown Hyperlinks</h2>

Hyperlinks in Markdown and HTML embedded documents can reference 
the root of the Fossil repository using the special text "$ROOT"
at the beginning of a URL. For example, a Markdown hyperlink to
the Markdown formatting rules might be
written in the embedded document like this:

<nowiki><pre>
        [Markdown formatting rules]($ROOT/wiki_rules)

Fossil will substitute the value of [./th1.md | TH1 expressions] within
<tt>{</tt> curly braces <tt>}</tt> into the output HTML if you have
configured it with the <tt>--with-th1-docs</tt> option, which is
disabled by default.

Since TH1 is a full scripting language, this feature essential grants
the ability to execute code on the server to any with check-in 
privilege for the project.
This is a security risk that needs to be carefully managed.
The feature is off by default.
Administrators should understand and carefully assess the risks
before enabling the use of TH1 within embedded documentation.