What Does A `.dtx` File Do? [duplicate]

Question

This question already has an answer here:

• What exactly happens when LaTeX runs on a dtx file? 1 answer

Latex documents often come with a number of different files. What does a .dtx file usually specify? Please assume that the person reading your answer has next to no experience with using LaTeX. I don't care about the syntax used inside of a .dtx, or how to write a .dtx, I just want a short explanation of what it does.

As an example, inside of a .dtx file put out by the association of computing machinery, I found the following:

% \begin{macro}{\if@ACM@screen}
%   Whether we use screen mode
%    \begin{macrocode}
\define@boolkey+{acmart.cls}[@ACM@]{screen}[true]{%
  \if@ACM@screen
    \PackageInfo{\@classname}{Using screen mode}%
  \else
    \PackageInfo{\@classname}{Not using screen mode}%
  \fi}{\PackageError{\@classname}{The option screen can be either true or
    false}}
\ExecuteOptionsX{screen=false}
%    \end{macrocode}
%
% \end{macro}

EDIT:
Originally I said that a .dtx was a "configuration file," and then asked what a .dtx did. However, others have informed me that a .dtx is not a "configuration file." I have subsequently edited the question.

Answer 1

*.dtx files are part of the doc system for specifying, packaging and documenting code. For full information (> texdoc doc) to view the manual. Essentially a .dtx file can consist of snippets of TeX code, textual explanations, user manual, etc. The snippets can be extracted from the file and placed in a number of output files to provide, say, a complete package, example uses of such a package, and a user manual. A single .dtx could contain the code for several packages each to be output as separate files.

It provides a way for code developers to basically wrap everything up into a single file rather than separate code, example, manual files which, if anything changed, would have to be updated separately (provided the coder remembered) whereas all can be done in a coordinated fashion in the .dtx

Mind you, creating a .dtx is not necessarily for the faint-hearted but most users need never see a .dtx as it is normally expanded.