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+# Rspamd composite rules
+
+Rspamd composites are used to combine rules and create more complex rules.
+Composite rules are defined by `composite` keys. The value of this key should be
+an object that defines composite's name and value, which is the combination of rules
+in a joint expression.
+
+For example, you can define a composite that is added when two of symbols are found:
+
+~~~nginx
+composite {
+	name = "TEST_COMPOSITE";
+	expression = "SYMBOL1 and SYMBOL2";
+}
+~~~
+
+In this case, if a message has `SYMBOL1` and `SYMBOL2` simultaneously then they are replaced by
+symbol `TEST_COMPOSITE`. The weights of `SYMBOL1` and `SYMBOL2` are substracted from the metric
+accordingly.
+
+## Composite expression
+
+You can use the following operations in a composite expression:
+
+* `AND` `&` - matches true only if both of operands are true
+* `OR` `|` - matches true if any of operands are true
+* `NOT` `!` - matches true if operand is false
+
+You also can use braces to define priorities. Otherwise operators are evaluated from left to right.
+For example:
+
+~~~nginx
+composite {
+    name = "TEST";
+    expression = "SYMBOL1 and SYMBOL2 and ( not SYMBOL3 | not SYMBOL4 | not SYMBOL5 )";
+}
+~~~
+
+Composite rule can include other composites in the body. There is no restriction of definition order:
+~~~nginx
+composite {
+    name = "TEST1";
+    expression = "SYMBOL1 AND TEST2";
+}
+composite {
+    name = "TEST2";
+    expression = "SYMBOL2 OR NOT SYMBOL3";
+}
+~~~
+
+Composites should not be recursive and it is normally detected by rspamd.
+
+## Composite weights rules
+Composites can leave the symbols in a metric or leave their weights. That could be used to create
+non-captive composites.
+For example, you have symbol `A` and `B` with weights `W_a` and `W_b` and a composite `C` with weight `W_c`.
+
+* If `C` is `A & B` then if rule `A` and rule `B` matched then these symbols are *removed* and their weights are removed as well, leading to a single symbol `C` with weight `W_c`.
+* If `C` is `-A & B`, then rule `A` is preserved, but the symbol `C` is inserted. The weight of `A` is preserved as well, so the total weight of `-A & B` will be `W_a + W_c`.
+* If `C` is `~A & B`, then rule `A` is *removed* but its weight is *preserved*, leading to a single symbol `C` with weight `W_a + W_c`
+