def scan(pattern, cons=false)
      return nil if @buffer.nil?
      rv = @buffer.scan(pattern)
      @buffer = $' if cons and rv.size>0
      rv
    end
def scan(pattern, cons=false)
      return nil if @buffer.nil?
      rv = @buffer.scan(pattern)
      @buffer = $' if cons and rv.size>0
      rv
    end
Scans the source for a given pattern.  Note, that this is not your
 usual scan() method.  For one thing, the pattern argument has some
 requirements; for another, the source can be consumed.  You can easily
 confuse this method.  Originally, the patterns were easier
 to construct and this method more robust, because this method
 generated search regexes on the fly; however, this was
 computationally expensive and slowed down the entire REXML package
 considerably, since this is by far the most commonly called method.
 @param pattern must be a Regexp, and must be in the form of
 /^\s*(#{your pattern, with no groups})(.*)/.  The first group
 will be returned; the second group is used if the consume flag is
 set.
 @param consume if true, the pattern returned will be consumed, leaving
 everything after it in the Source.
 @return the pattern, if found, or nil if the Source is empty or the
 pattern is not found.