symbols verses words

[Perry Smith]

I need some help understanding Emac's design.  I use a lot of "word" constructs 
where I *think* I should be using symbol.  For example, if I'm writing C code 
and I want to find foo but not foo_bar, I usually do \<foo\> but really it 
seems that I should be doing \_<foo\_> ... fine.  I can make that adjustment.  
But when I do incremental search, I often hit ^w to pull in the next word but 
what I really want (often but not always) is to pull in the next symbol (into 
the search string).  So if I'm sitting at this_that, I'd ilke to hit ^W 
(perhaps) and pull in this_that instead of just this.

So, I started looking at isearch-yank-word-or-char and I was going to concoct 
isearch-yank-symbol-or-char and got stuck-- at least briefly.  Because not only 
is _ marked as symbol, -, +, /, *, etc are marked as symbol characters too.  So 
now, I'm confused...

If I have:  this  this_that  this-that

and search for \_<this\_> I hit the first and third this -- which is exactly 
what I want.  But how is it doing that since this_that and this-that are the 
same as far as looking at the syntax table entries?  They are both wwww_wwww.

I'd like to understand how the \_< and \_> constructs work so I can make my 
isearch-yank-symbol-or-char work in a consistent manner.

Thanks,
Perry