diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index 72967deb78..8579530710 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines
@@ -376,7 +376,10 @@ For C programs:
    string_list for sorted string lists, a hash map (mapping struct
    objects) named "struct decorate", amongst other things.
 
- - When you come up with an API, document it.
+ - When you come up with an API, document its functions and structures
+   in the header file that exposes the API to its callers. Use what is
+   in "strbuf.h" as a model for the appropriate tone and level of
+   detail.
 
  - The first #include in C files, except in platform specific compat/
    implementations, must be either "git-compat-util.h", "cache.h" or