xenvironment place holders

Hi,

We noticed that on the action.properties and on environment.properties we see some placeholders like these ones:

%{e:environment.dir.root}/ext/set_time.

%{s:script.extension}

%{b:xstore-thin-client.disabled}

%{p:root.dir}/updates

But in the documentation havent found any references to them, is there any document that explain them (including why some times first letter is %{s, %{e, %{p, %{b and also where those properties are defined on? e.g: couldnt found where environment.dir.root is defined)

Thanks, Best Regards.