Book abbreviations (TOC3) - typesetting restrictions?

Question

When it comes to book abbreviations (TOC3), the help page on “Best practice for choosing abbreviations for book names” underlines the importance of consistency within a project. So provided a given project is consistent within itself, are there any restrictions on book abbreviations for typesetting/publishing? For example, must the book abbreviation be composed of a certain number of characters (e.g., three)? Are spaces permitted? Are acronyms and initialisms permitted? I ask because functionally Paratext seems to have no problem with any of these.

Answer 1

Technically there are no restrictions on any of the TOC marker contents except that you cannot have the book names the same for two different books. The most common issue is the abbreviations for books that have similar names like John and Jonah, and Philippians and Philemon.

Another issue is if you put the number for John’s epistles after the name you can end up with reference errors. For example like this:
JHN \toc2 John
1JN \toc2 John 1
2JN \toc2 John 2
3JN \toc2 John 3

With these
\r John 1:1-15
will create a reference error.
My solution is to put a no-break space in the Johannine epistle names:
1JN \toc2 John~1
2JN \toc2 John~2
3JN \toc2 John~3

That said, you need to know how you want to use these different ways of referencing books. If you are creating center column cross-references you need very short \toc3 abbreviations. But if you only want cross-references in footnotes you can use whatever you want. You can even make \toc1 \toc2 and \toc3 the same and Paratext will not complain.