[PATCH v2 4/8] man: clarify search --exclude documentation

[Peter Wang <novalazy@gmail.com>]

Highlight "excluded messages" as a term with a meaning that
may not be obvious.

Be explicit about the effects of search --exclude=true and
--exclude=false.
---
 man/man1/notmuch-search.1 |   15 +++++++++++++--
 1 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/man/man1/notmuch-search.1 b/man/man1/notmuch-search.1
index 5c72c4b..52782c7 100644
--- a/man/man1/notmuch-search.1
+++ b/man/man1/notmuch-search.1
@@ -116,8 +116,19 @@ Limit the number of displayed results to N.
 .TP 4
 .BR \-\-exclude=(true|false|flag)
 
-Specify whether to omit messages matching search.tag_exclude from the
-search results (the default) or not. The extra option
+A message is called "excluded" if it matches at least one tag in
+search.tag_exclude that does not appear explicitly in the search terms.
+This option specifies whether to omit excluded messages in the search
+process.
+
+The default value,
+.BR true ,
+prevents excluded messages from matching the search terms.
+
+.B false
+allows excluded messages to match search terms and appear in displayed
+results. Excluded messages are still marked in the relevant outputs.
+
 .B flag
 only has an effect when
 .B --output=summary
-- 
1.7.4.4