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+Adding new libraries
+====================
+
+When adding a new sub-library to OpenSSL, assign it a library number
+`ERR_LIB_XXX`, define a macro `XXXerr()` (both in `err.h`), add its
+name to `ERR_str_libraries[]` (in `crypto/err/err.c`), and add
+`ERR_load_XXX_strings()` to the `ERR_load_crypto_strings()` function
+(in `crypto/err/err_all.c`). Finally, add an entry:
+
+    L      XXX     xxx.h   xxx_err.c
+
+to `crypto/err/openssl.ec`, and add `xxx_err.c` to the `Makefile`.
+Running make errors will then generate a file `xxx_err.c`, and
+add all error codes used in the library to `xxx.h`.
+
+Additionally the library include file must have a certain form.
+Typically it will initially look like this:
+
+    #ifndef HEADER_XXX_H
+    #define HEADER_XXX_H
+
+    #ifdef __cplusplus
+    extern "C" {
+    #endif
+
+    /* Include files */
+
+    #include <openssl/bio.h>
+    #include <openssl/x509.h>
+
+    /* Macros, structures and function prototypes */
+
+
+    /* BEGIN ERROR CODES */
+
+The `BEGIN ERROR CODES` sequence is used by the error code
+generation script as the point to place new error codes, any text
+after this point will be overwritten when make errors is run.
+The closing `#endif` etc will be automatically added by the script.
+
+The generated C error code file `xxx_err.c` will load the header
+files `stdio.h`, `openssl/err.h` and `openssl/xxx.h` so the
+header file must load any additional header files containing any
+definitions it uses.
+
+Adding new error codes
+======================
+
+Instead of manually adding error codes into `crypto/err/openssl.txt`,
+it is recommended to leverage `make update` for error code generation.
+The target will process relevant sources and generate error codes for
+any *used* error codes.
+
+If an error code is added manually into `crypto/err/openssl.txt`,
+subsequent `make update` has no effect.