--- trunk/doc/exact_match.txt	2003/11/29 19:11:23	190
+++ branches/ffzg/doc/exact_match.txt	2004/04/04 22:11:13	303
@@ -20,10 +20,37 @@
 6:	exact from end with wild-card	"human* xxexx"
 7:	exact begin+end with wild-card	"xxbxx human* xxexx"
 
-So, to define field which have to search using exact match with wild-card
+So, to define field which have to be searched using exact match with wild-card
 on TitleAndResponsibility, you would use:
 
 <input type="hidden" name="f1" value="TitleAndResponsiblity">
 <input type="text" name="v1">
 <input type="hidden" name="e1" value="5">
 
+
+What are bit-masks?
+
+Bit-mask is usage of one byte (8 bits) as 8 separate bits with it's own
+meaning (this is simplification, but bear with me for now).
+
+So, 1 = 2^0, thus it's bit 1. With analogy, 2=2^1 and 3=2^0+2^1. 
+So, for 1-3 we use two bits and have:
+
+number	bits
+1	01	(just begin bit set)
+2	10	(just end bit set)
+3	11	(begin and end bit set)
+
+Thus, with two bits (and values 1-3) we can express should we exact match from
+beginning, end or both. For wild-card match, we use additional bit 3 (2^3 = 4)
+so we have:
+
+number	bits	exact match
+1	001	begin
+2	010	end
+3	011	begin+end
+4	100	(not used)
+5	101	(4+1) begin+wild-card
+6	110	(4+2) end+wild-card
+7	111	(4+3) begin+end+wild-card
+