diff --git a/config.md b/config.md
index 0a21d654d..5af076a13 100644
--- a/config.md
+++ b/config.md
@@ -2,6 +2,7 @@
 
 The container's top-level directory MUST contain a configuration file called `config.json`.
 The canonical schema is defined in this document, but there is a JSON Schema in [`schema/config-schema.json`](schema/config-schema.json) and Go bindings in [`specs-go/config.go`](specs-go/config.go).
+For properties that are only defined for some [protocols](README.md#compliance), the Go property has a `platform` tag listing those protocols (e.g. `platform:"linux,solaris"`).
 
 The configuration file contains metadata necessary to implement standard operations against the container.
 This includes the process to run, environment variables to inject, sandboxing features to use, etc.