Substring matched by regex

[Aaron Maxwell]

In a function, how do I get the value of a string matched by a regex?

In a function I'm writing, I need to parse the first bit of text matching a 
certain regex prior to point.  re-search-backward will get the start and end 
positions of that string (accessible to me via match-data), but I need a 
function that will get the actual text as a string.  Something 
like "str-from-current-buffer" in this snippet:

(defun fetch-text-to-parse ()
  (interactive)
  (save-excursion
    (progn
      (re-search-backward "regexp.to.match")
      (str-from-current-buffer (car (match-data)) (cadr (match-data))))))

copy-region-as-kill will kind of work, but it smells like a hack and (more 
importantly) pollutes the kill ring.  Could someone point me to a good way to 
do what I'm trying to do here?

Thanks much.

-- 
Aaron Maxwell
http://redsymbol.net

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