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-rw-r--r--doc/bird.sgml2
1 files changed, 2 insertions, 0 deletions
diff --git a/doc/bird.sgml b/doc/bird.sgml
index ff599216..90ceb184 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -5094,6 +5094,8 @@ Bitmask matching is written using <m/value/<cf>/</cf><m/mask/ or
<cf/!/<m/value/<cf>/</cf><m/mask/ pairs. It means that <cf/(/<m/data/ <cf/&/
<m/mask/<cf/)/ is or is not equal to <m/value/. It is also possible to use
multiple value/mask pairs connected by logical operators <cf/&&/ or <cf/||/.
+Note that for negated matches, value must be either zero or equal to bitmask
+(e.g. !0x0/0xf or !0xf/0xf, but not !0x3/0xf).
<sect2>IPv4 Flowspec