id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
13156	Not word boundary -  \b   vs. NOT \B are not the same	anonymous	John Maddock	"I am reposting this from another source. 

In theory, \B should match everywhere \b doesn't.  

In boost regex, this is not the case at the beginning nor end of string.  

Below is a list of test results from a few Perl-like engines.  
Apparently, this was fixed in Perl v5.22 (below shows v5.20).  
The only engines that seem to handle this correctly is PHP and
ECMAScript.  

------------------------------------------------

{{{

Target      = '   ssssssssssssss '
Replacement = '<>'

==================================================
PHP 7.03

\b      = '   <>ssssssssssssss<> '
\B      = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\b)  = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?<!\b) = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\B)  = '   <>ssssssssssssss<> '
(?<!\B) = '   <>ssssssssssssss<> '


=======================================
Perl 5.20

\b      = '   <>ssssssssssssss<> '
\B      = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s '
(?!\b)  = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?<!\b) = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\B)  = '   <>ssssssssssssss<> '
(?<!\B) = '   <>ssssssssssssss<> '

========================================
Boost 1.64

\b      = '   <>ssssssssssssss<> '
\B      = ' <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s '
(?!\b)  = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?<!\b) = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\B)  = '<>   <>ssssssssssssss<> <>'
(?<!\B) = '<>   <>ssssssssssssss<> <>'

=====================================
JavaScript

\b      = '   <>ssssssssssssss<> '
\B      = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\b)  = '<> <> <> s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s<>s <>'
(?!\B)  = '   <>ssssssssssssss<> '

}}}
"	Bugs	new	To Be Determined	regex	Boost 1.64.0	Showstopper		Not Word Boundary \B