How were leaders (before-the-scene and cut-in) and inserts (letters, telegrams, news items) written into a 1913-era numbered continuity, when did the authors say to use them, and what cautions do they give?

The authors define a leader (sub-title before a scene), a cut-in (dialogue leader inside a scene) and an insert (letter, telegram, news item shown inside a scene), and give notation: a before-scene leader is written ahead of the numbered scene; a letter is flagged "On screen, letter", given in full, then closed with "Back to scene"; busts and close-ups get their own scene numbers. They say to use inserts only when action cannot make the point, to prefer a letter or news item over a plain leader, to avoid a leader straight after the title, and not to under-use leaders either. Label: 1913 practice. The pinned Gutenberg text is the Revised Edition (title page "Copyright 1913 / Copyright 1919"; it mentions 1918 releases and "February, 1919" postage), so some passages are 1919 revisions and are not 1913 practice. Excerpts drop Gutenberg italic underscores; line numbers are those of the CRLF file as pinned. Curator qualifications: Word-on-screen devices and notation verified; limits are qualitative. Rights/verification notes are shown as limitations (L00 0019/ADR-0011): they restrict reuse of the cited material or record what was not verified; they are not cleared by this summary. Limitations: [component_reuse_restriction] Producer work dir holds no copy of S1; curator fetched Project Gutenberg #17903 (Esenwein & Leeds, Writing the Photoplay, 1913 rev. 1919; US public domain), byte-identical to pin 7a6b66f7, and located all 55 S1 excerpts after normalising quotes/underscores/whitespace. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://www.gutenberg.org/cache/epub/17903/pg17903.txt",
      "note": "Writing the Photoplay"
    }
  ]
}