explain whitespace pattern

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/lang/trunk@1407537 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/lang3/StringUtils.java

@@ -150,6 +150,11 @@ public class StringUtils {
 
     /**
      * A regex pattern for recognizing blocks of whitespace characters.
+     * The apparent convolutedness of the pattern serves the purpose of
+     * ignoring "blocks" consisting of only a single space:  the pattern
+     * is used only to normalize whitespace, condensing "blocks" down to a
+     * single space, thus matching the same would likely cause a great
+     * many noop replacements.
      */
     private static final Pattern WHITESPACE_PATTERN = Pattern.compile("(?: \\s|[\\s&&[^ ]])\\s*");