diff --git a/docs/devel/memory.txt b/docs/devel/memory.txt
index 4fff0d560311dd63af39b9b58501949465bddbf8..42577e1d860e46d2dfed9936cb45aa42a9fd309d 100644
--- a/docs/devel/memory.txt
+++ b/docs/devel/memory.txt
@@ -326,8 +326,15 @@ visible as the pci-hole alias clips it to a 0.5GB range.
 MMIO Operations
 ---------------
 
-MMIO regions are provided with ->read() and ->write() callbacks; in addition
-various constraints can be supplied to control how these callbacks are called:
+MMIO regions are provided with ->read() and ->write() callbacks,
+which are sufficient for most devices. Some devices change behaviour
+based on the attributes used for the memory transaction, or need
+to be able to respond that the access should provoke a bus error
+rather than completing successfully; those devices can use the
+->read_with_attrs() and ->write_with_attrs() callbacks instead.
+
+In addition various constraints can be supplied to control how these
+callbacks are called:
 
  - .valid.min_access_size, .valid.max_access_size define the access sizes
    (in bytes) which the device accepts; accesses outside this range will