\b will match between a \w character and a \W character and \B will match between two \w characters or between two \W characters. 

I have tried
print if /\B.\d+.\d+\s+.?\s+\B/;
print if /\B.\d+.\d+\s+.?\s+\B/FA;
print if /\B.\d+\s+\w+\B/FA;

[download]

Your examples start off with \B.\d+ which says match at a \B boundary then match any character (except newline) then match one or more digits.    So if the any character before the digits is a \w character then there must be at least two \w characters before the digits or if the any character before the digits is a \W character then there must be at least two \W characters before the digits.

The only strings in your example that will match that pattern are "c10" or "0t2" or "2d1".

In reply to Re: boundries \b \B by jwkrahn
in thread boundries \b \B by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.