We ask that writers post no more than the first thirteen lines (in manuscript format using 12-point courier font) of any story here on the Hatrack website for very good reasons.
First, it protects the writer's electronic rights to the story, and it still gives readers the "first page" of a story in manuscript format.
Second, since many editors only read the first page of a manuscript anyway (deciding from that much whether the story is interesting enough to continue reading), Hatrackers should be able to make a similar judgment on your story openings.
If you set up your manuscript properly, you will double-space between each line of text, giving you 25 or 26 lines on each page.
The first page of each manuscript should start the text halfway down the sheet of paper, to allow room for the name, address, word count, title, byline, and room for the editor to make notes to the typesetter as needed.
So the first page of a properly presented manuscript only has 13 lines on it.
That's for a short story manuscript, though. Novel chapters can start closer to the top because a novel has a separate title page with just the name, address, word count, title and byline--plenty of room for editorial notes to the typesetter.
Anyway, the first 13 lines implies the first page, and many editors will only read the first page of a manuscript before deciding to reject or to read on.
Now, for the electronic rights question. Even though most publishers are not likely to make use of the electronic rights to a story, for several years now, they have insisted on controlling an author's electronic rights and have included "deal-breaker" clauses about those rights in every contract.
New writers, who have no clout, must agree to let the publisher control electronic rights in order to make a sale--novel or short story.
If the electronic rights have already been used up by the author, by publishing the story on a website (which is accessible to the whole world) for example, then the publisher can't control electronic rights. Unless the author's work has phenomenal sales potential (as in the case of some self-published works such as THE CHRISTMAS BOX), the publisher is not going to be interested in publishing a story or novel without that control. Even if publishers don't have any use for electronic rights right now, they anticipate having use for them in the future and don't want to have to negotiate for them later.
This is the way we determine if a story fragment is 13 lines or not:
First we highlight the text and copy it to the computer clipboard. Then we paste it into a manuscript template in MS Word, with Courier New font set at 12. Then we count the lines. If the sentence in the 13th line is only a little longer, we let the text go over 13 lines.
Finally, we go back to the topic and delete all but the actual, MS-Word-manuscript-format-12-point-font 13 lines.