docs(CONTRIBUTING): describe naming convention

CONTRIBUTING.md

@@ -193,6 +193,44 @@ commits for respective purposes.  On the other hand, PRs including several
 minor fixes to the exiting codebase will not be squashed because each commit
 gives a separate fix to the exiting code.
 
+### Naming convention of functions and global variables
+
+Initially, we haven't cared about the naming convention very much, but we now
+try to improve it.  In particular, the new codes should follow this naming
+convention.  The contributions to improve old codes are also welcome, but we
+also need to keep the backward compatibility.  See [Discussion
+#280](https://github.com/ohmybash/oh-my-bash/discussions/280) for background.
+
+The functions/aliases that are supposed to be used as interactive commands can
+have arbitrary names including short ones.
+
+The functions that are used from the other functions have the names of the form
+`_omb_*`.
+
+* The functions defined by libraries has the form `_omb_${namespace}_${funcname}`
+* The functions defined by a specific plugin has the form `_omb_plugin_${plugin_name}_${funcname}`
+* The functions defined by a specific theme has the form `_omb_theme_${theme_name}_${funcname}`
+* Some important functions might have the name `_omb_${funcname}` directly put under `_omb` namespace.
+
+Public global variables that can be used to configure the behavior of
+oh-my-bash have the form `OMB_*`.
+
+* The settings for the main oh-my-bash behavior have the names of the form `OMB_${config^^}`
+* The settings for the detailed behavior have the names of the form `OMB_${namespace^^}_${config^^}`
+* The settings for a specific plugin has the form `OMB_PLUGIN_${plugin_name^^}_${config^^}`
+* The settings for a specific theme has the form `OMB_THEME_${theme_name^^}_${config^^}`
+
+Internal global variables put into global variables used by oh-my-bash has the form `_omb_*`
+
+* The internal variables defined by libraries has the form `_omb_${namespace}_${varname}`
+* The internal variables used by a specific plugin has the form `_omb_plugin_${plugin_name}_${varname}`
+* The internal variables used by a specific theme has the form `_omb_theme_${theme_name}_${varname}`
+* Some important variables might have the name `_omb_${varname}` directly put under `_omb` namespace.
+
+There are no restrictions on the local variable names.  A prefix like
+`_omb_${namespace}_` is unnecessary because the namespace of the local
+variables is separated for each function call.
+
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