diff --git a/library/ecp.c b/library/ecp.c
index e3b9106..d9a3ac2 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -47,6 +47,35 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
+/**
+ * \brief Function level alternative implementation.
+ *
+ * The MBEDTLS_ECP_INTERNAL_ALT macro enables alternative implementations to
+ * replace certain functions in this module. The alternative implementations are
+ * typically hardware accelerators and need to activate the hardware before the
+ * computation starts and deactivate it after it finishes. The
+ * mbedtls_internal_ecp_init() and mbedtls_internal_ecp_free() functions serve
+ * this purpose.
+ *
+ * To preserve the correct functionality the following conditions must hold:
+ *
+ * - The alternative implementation must be activated by
+ *   mbedtls_internal_ecp_init() before any of the replaceable functions is
+ *   called.
+ * - mbedtls_internal_ecp_free() must \b only be called when the alternative
+ *   implementation is activated.
+ * - mbedtls_internal_ecp_init() must \b not be called when the alternative
+ *   implementation is activated.
+ * - Public functions must not return while the alternative implementation is
+ *   activated.
+ * - Replaceable functions are guarded by \c MBEDTLS_ECP_XXX_ALT macros and
+ *   before calling them an \code if( mbedtls_internal_ecp_grp_capable( grp ) )
+ *   \endcode ensures that the alternative implementation supports the current
+ *   group.
+ */
+#if defined(MBEDTLS_ECP_INTERNAL_ALT)
+#endif
+
 #if defined(MBEDTLS_ECP_C)
 
 #include "mbedtls/ecp.h"