Re: Make \< and \> match symbol boundaries

[Richard Stallman]

      \_< is like \<
      \_> is like \>
      \_b is like \b
      \_B is like \B
      \_w is like \w
      \_W is like \W

      except that in each case, the variant with `_' uses symbols not words.

I like this approach.

Meanwhile, for more generality, we might want to implement this more
general idea as well:

    Here's another idea: generalize the existing regexps \b, \B, etc. to
    support arbitrary classes and syntaxes, not just word syntax.  For
    example, to generalize \b we could add the following regexps:

    \-bsC matches the empty string, but only at the beginning or end of a
          sequence of one or more characters whose syntax is C.
    \-bSC matches the empty string, but only at the beginning or end of a
          sequence of one or more characters whose syntax is not C.
    \-bcC matches the empty string, but only at the beginning or end of a
          sequence of one or more characters that belongs to the category C.
    \-bCC matches the empty string, but only at the beginning or end of a
          sequence of one or more characters that do not belong to the category 
C.

    \b is equivalent to \-bsw.

    If we take this approach, then \-<s_ and \->s_ would have the desired
    interpretation of matching symbol boundaries.

but using a set of classes or categories rather than just one.

Or we could just write down this plan, and implement it later
if it seems useful enough.