Issue #2054 has been updated by Yui NARUSE.


+ *  literally backslash-escape that: <tt>\\\\\\</tt>.
Why 6 times?

+ *  * <tt>/\d/</tt> - A digit character (<tt>[0-9]</tt>)
+ *  * <tt>/\D/</tt> - A non-digit character (<tt>[^0-9]</tt>)
Add following:
 *  * <tt>/\h/</tt> - A hexdigit character (<tt>[0-9a-fA-F]</tt>)
 *  * <tt>/\H/</tt> - A non-hexdigit character (<tt>[^0-9a-fA-F]</tt>)

+ *  * <tt>{n,}</tt> - n or more times
Add *  * <tt>{,m}</tt> - m or less times

== Grouping

(?: ..) should be introduced also in this chapter.

+ *  Capture groups can be referred to by name when defined with the
+ *  <tt>(?<name>)</tt> construct.

Don't mention an alias (?'name'subexp) ?

+ *      /£(?<pounds>\d+)\.(?<pence>\d+)/.match("£3.67")
Pound Sign (U+00A3) is non-ASCII.
Dollar Sign (U+0024) is in ASCII (but Cent Sign is non-ASCII).

+ *    characters match <i>pat</i>, but doesn¡Çt include those characters in the 
Right Single Quotation Mark (U+2019) is non-ASCII
Apostrophe (U+0027) is in ASCII.

+ *  A regexp can be matched only against a string whose encoding is the
+ *  same as, or a superset of, the regexp's encoding. If a match between

The word "superset" is misleading.
In Ruby 1.9, this relation is only US-ASCII and other ASCII-compatible encodings.
So "or regexp's encoding is US-ASCII and string's encoding is ASCII-compatible".

+ *  The <tt>Regexp#fixed_encoding?</tt> predicate indicates whether the regexp
Needs encoding modifiers set FIXED_ENCODING.
And /n doesn't set FIXED_ENCODING but warn.
  irb(main):001:0> /a/n=~"a\u3042"
  (irb):1: warning: regexp match /.../n against to UTF-8 string
  => 0


Don't mention following?
*  x-y     range from x to y
* ..&&..  intersection (low precedence at the next of ^)
* reluctant and possessive quantifier
* atomic group (?>subexp) 
* back reference \k<..>
* subexp call \g<..>
* substitution by literarl regexp matching
  /(?<foo>b\w+)/ =~ 'bar' #=> 0
  foo #=> "bar"

If you can describe about  /(a|b+)*/ , it will be helpful.
http://www.ruby-forum.com/topic/70726
----------------------------------------
http://redmine.ruby-lang.org/issues/show/2054

----------------------------------------
http://redmine.ruby-lang.org