I have a question about document structure, because I want to structure a series of products correctly and I do not know if I understand everything in the manual about it well enough. 

Must I understand that "\startlocalenvironment[abc]" within an environment file means that this codeblock is used only for typesetting product/component abc and excluded automatically when another product/component is typeset?

Or is it just a declaration analogous to "\startenvironment file setups \stopenvironment"?

But then I don't understand why the manual does not tells me 

"\startlocalenvironment[abc] file setups \stoplocalenvironment" as it does for \startenvironment

The macro "\localenvironment name" gives me some headaches. I might guess usage in a master setup file as:

\localenvironment abc % load environment file abc.tex if typesetting product/component abc