[PATCH v2 5/7] doc: add some more documentation on bitmasks

[Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>]

Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
---
 doc/data-types.txt | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/doc/data-types.txt b/doc/data-types.txt
index 18af266a..47a0d25a 100644
--- a/doc/data-types.txt
+++ b/doc/data-types.txt
@@ -26,6 +26,22 @@ integer
 
 The bitmask type (*bitmask*) is used for bitmasks.
 
+In expressions the bits of a bitmask may be specified as *'bit'[,'bit']...* with
+'bit' being the value of the bit or a pre-defined symbolic constant, if any (for
+example *ct state*’s bit 0x1 has the symbolic constant `new`).
+
+Equality of a value with such bitmask is given, if the value has any of the
+bitmask’s bits set (and optionally others).
+
+The syntax *'expression' 'value' / 'mask'* is identical to
+*'expression' and 'mask' == 'value'*.
+For example `tcp flags syn,ack / syn,ack,fin,rst` is the same as
+`tcp flags and (syn|ack|fin|rst) == syn|ack`.
+
+It should further be noted that *'expression' 'bit'[,'bit']...* is not the same
+as *'expression' {'bit'[,'bit']...}*.
+
+
 STRING TYPE
 ~~~~~~~~~~~~
 [options="header"]
-- 
2.51.0