Better document version ranking and 0

Document that an empty Debian revision is equivalent to a Debian
revision of 0 and clarify the way version numbers are compared.  Thanks
to Raphael Hertzog for information about what dpkg does.

diff --git a/policy.sgml b/policy.sgml
index 1c9a3394764304c9f15d42ff93329c302cfeae1a..b7ac92e64a4c7b0f79ac8c667d792e2c1d4dfcf7 100644 (file)
--- a/policy.sgml
+++ b/policy.sgml
@@ -2877,19 +2877,22 @@ Package: libc6
                  number apart at the last hyphen in the string (if there
                  is one) to determine the <var>upstream_version</var> and
                  <var>debian_revision</var>.  The absence of a
-                 <var>debian_revision</var> compares earlier than the
-                 presence of one (but note that the
-                 <var>debian_revision</var> is the least significant part
-                 of the version number).
+                 <var>debian_revision</var> is equivalent to a
+                 <var>debian_revision</var> of <tt>0</tt>.
                </p>
              </item>
            </taglist>
          </p>
 
          <p>
-           The <var>upstream_version</var> and <var>debian_revision</var>
+           When comparing two version numbers, first the <var>epoch</var>
+           of each are compared, then the <var>upstream_version</var> if
+           <var>epoch</var> is equal, and then <var>debian_revision</var>
+           if <var>upstream_version</var> is also equal.
+           <var>epoch</var> is compared numerically.  The
+           <var>upstream_version</var> and <var>debian_revision</var>
            parts are compared by the package management system using the
-           same algorithm:
+           following algorithm:
          </p>
 
          <p>