Explain the source file the user points you at (a file or the current code view).

Cover:

  1. Its purpose in one or two sentences.
  2. The key exports/functions/classes and what each does.
  3. Notable dependencies and how this file is used by others, if you can tell.
  4. Any gotchas or non-obvious logic worth flagging.

Use plain language; reference real symbol names. Don't reproduce the whole file.