added more detail to regex match all, and problem clarified

Author: brigand

chapters/regular_expressions/finding-all-matches.md

@@ -7,6 +7,13 @@ chapter: Regular Expressions
 
 You need to find all matches, not just the first.
 
+For example,
+
+{% highlight coffeescript %}
+/\d+/g.exec "I have 4 dogs, 7 cats, and 42 gold fish."
+# => ["4"]
+{% endhighlight %}
+
 ## Solution
 
 {% highlight coffeescript %}
@@ -32,6 +39,29 @@ RegExp::execAll = (haystack) ->
 # => [["4 dogs","4","dogs"],["7 cats","7","cats"],["42 gold","42","gold"]]
 {% endhighlight %}
 
-The first line of `execAll` prevents an infinite loop caused by non-global expressions.  This could be further improved by creating a clone of the RegExp that is global, and use that.
+The first line of `execAll` prevents an infinite loop caused by non-global expressions.  This could be further 
+improved by creating a clone of the RegExp that is global, and use that.
 
+You must not save a reference to this expression (like `a = /xyx/g`) if you plan to call `execAll` more than once.  
+The same behavior be observed with the regular `exec` method.
+
+{% highlight coffeescript %}
+s = "I have 4 dogs, 7 cats, and 42 gold fish."
+myRegEx = /\d+/g
+myRegEx.exec s
+# => ["4"]
+myRegEx.execAll s
+# => ["7", "42"]
+myRegEx.exec s
+# => null
+{% endhighlight %}
+
+Instead use:
+
+{% highlight coffeescript %}
+/\d+/g.execAll s
+# => ["4", "7", "42"]
+/\d+/g.execAll s
+# => ["4", "7", "42"]
+{% endhighlight %}