README on parameters

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diff --git a/README.md b/README.md
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--- a/README.md
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@@ -10,3 +10,43 @@ License
 This project is under the MIT license (see [LICENSE](LICENSE)),
 unless stated otherwise in individual files.
 
+
+Ideas
+=====
+
+
+Parametrization
+---------------
+
+Everything that _can_ be used at build time should have a parameter (integer,
+string, path, etc.).  Examples are TCP port, data directory, UNIX user. TCP
+port can be used for configuring firewall or HTTP proxy, data directory can
+be used for setting up mount points, UNIX user can be included into extra
+groups, etc.  When we have it all parametrized we do not repeat ourselves.
+
+Parametrization also helps modularity. I. e. you can define default set of
+values and override only some of them in specific setups.
+
+Some applications accept only discrete set of options, in that case we should
+parametrize them all.  Examples are memcached, php-fpm and sproxy2.
+
+Parametrization should give access to all application features. Ideally,
+parameters should exactly match to the application options, including
+their names and meanings.  Examples are MariaDB and PostgreSQL. This makes
+documentation unnecessary, because each parameter is documented somewhere else.
+
+Almost every parameter, if it's not required by application (i. e. has
+a built-in default value), should have value `null` by default.  If such
+parameter is not set, it is not passed to the application. This is twofold:
+more transparency because we use _application's_ defaults (not ours), and it
+is safer to use different versions of application, when particular options
+may be added or removed.
+
+Even though, if the value of parameter is required at build time, the parameter
+should have default value, preferably application's default. Example is
+MariaDB's TCP port. We need it to configure firewall, thus we define it to
+be 3306 by default.
+
+If application default value is known to be insecure, we should set our own,
+_secure_, default value.
+