add a paragraph clarifying use of 'and' and 'or'

diff --git a/doc/pagespec.mdwn b/doc/pagespec.mdwn
index e004de4af9a0e7238e9bac017b1a1ad064e512fc..5c6433ed3391337aaf5d3cd1afea0057e0aa2042 100644 (file)
--- a/doc/pagespec.mdwn
+++ b/doc/pagespec.mdwn
@@ -41,6 +41,12 @@ and were written in 2005:
 
        blog/* and link(music) and creation_year(2005)
 
+Note the use of "and" in the above example, that means that only pages that
+match each of the three expressions match the whole. Use "and" when you
+want to combine expression like that; "or" when it's enough for a page to
+match one expression. Note that it doesn't make sense to say "index and
+SandBox", since no page can match both expressions.
+
 More complex expressions can also be created, by using parentheses for
 grouping. For example, to match pages in a blog that are tagged with either
 of two tags, use: