Scans the string until the pattern is matched. Returns the matched string if return_string_p is true, otherwise returns the number of bytes advanced. Advances the scan pointer if advance_pointer_p, otherwise not. This method does affect the match register."

But consider these (edited) results...

irb(main):005:0> a='abc .r def .n'
=> "abc .r def .n"
irb(main):009:0> aa=StringScanner.new(a)
=> #<StringScanner 0/13 @ "abc ....">
irb(main):014:0> aa.search_full(/\.r /,true,false)
=> 7
irb(main):016:0> aa.pos
=> 7

[comment: these results are the opposite of what I expected - I did NOT get back the matched string, and the pointer WAS advanced.]

irb(main):021:0> aa.reset
=> #<StringScanner 0/13 @ "abc ....">
irb(main):022:0> aa.search_full(/\.r /,false,true)
=> "abc .r "
irb(main):023:0> aa.pos
=> 0

[comment: again - this is the opposite of what I expected, given the documentation.]

irb(main):025:0> a
=> "abc .r def .n"

Environment:
OS: Kubuntu Linux 8.10 Intrepid Ibix
/$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]