This book documents Version 1.6 of Ruby, which was released in September
Ruby version numbering follows the same scheme used for many other open source
projects. Releases with even subversion numbers (1.0, 1.2, 1.4, and
so on) are stable, public releases. These are the releases that are
prepackaged and made available on the various Ruby Web sites.
Development versions of the software have odd subversion numbers,
such as 1.1 and 1.3. These you'll have to download and build for
yourself, as described in the box on page xxvii.