diff --git a/core/insurance.xml b/core/insurance.xml
index c5203dd4..64f93dc9 100644
--- a/core/insurance.xml
+++ b/core/insurance.xml
@@ -288,4 +288,136 @@
+
+
+ The \ref{_credit_} and \ref{_debit_} templates define factors that are
+ intended to introduce, respectively, credits and surcharges.
+ Each name defined using these templates must be prefixed with ``credit''
+ and ``debit'' respectively.
+ Credits must never exceed a value of~$1$,
+ as they would then be treated as if they were surcharges.
+ Similarly, debits must never have a value less than~$1$.
+ Both must have values greater than~$0$.
+
+ If a value can be either a credit or a debit,
+ it is sometimes called an ``adjustment''.
+ In reality it is just another factor,
+ so just use \ref{_factor_} in such a~case.
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