character macro in biber file

Question

We're using a bibtex file in XeLaTeX + biblatex that was originally encoded in ASCII, so accented characters are represented by macros. The rest of the text is Unicode UTF-8. One of the accented characters in the .bib file is \"{0}, which XeLaTeX deals with just fine (and this is the way of representing such characters I see in places like https://en.wikibooks.org/wiki/LaTeX/Special_Characters#Escaped_codes. But biber complains:

ERROR - BibTeX subsystem: /tmp/i_hu76qDT8/References.bib_3533.utf8, 
line 2, syntax error: found "{o}", expected end of entry ("}" or ")") 
(skipping to next "@")
INFO - ERRORS: 1

Biber apparently wants the format {\"o}, which XeLaTeX also accepts.

We normally use UTF-8 everywhere, rather than ASCII escaped characters. But when importing old .bib files, we haven't been bothering to convert the escaped character codes to UTF-8--at least until now. In fact I know this worked without our converting the codes for several years; it must be a recent change to biber that broke the \"{o} representation. (We now have biber v2.10.)

Is this expected, or a bug? Minimal example follows. It "compiles" ok in XeLaTeX, but the biber step fails with the above error msg.

===========XeLaTeX file==========

\documentclass{report}
\usepackage{biblatex}
\addbibresource{References.bib}

\begin{document}
John S\"{o}ren wrote \cite{TestEntry}.
\printbibliography
\end{document}

==========.bib file============

@InCollection{TestEntry,
   author    = "John S\"{o}ren",
   booktitle = "Nonesuch",
   publisher = "Some Publisher",
   address   = "Somewhere",
   year      = "1996"
}

Answer 1

I'm afraid it has never been right to write

author    = "John S\"{o}ren",

in a .bib file - things are different in a normal .tex file, that's what the Wikibook page you linked to applies to.

There are only very few differences between "..." and {...} as field delimiters for .bib files, but one of them is that fields enclosed in "..." can't have an unprotected " in the field contents. Within "..." literal "s have to be protected by enclosing them in braces. This is one of the reasons why you must write {\"o} and not \"{o} in .bib files, see How to write “ä” and other umlauts and accented letters in bibliography? as well as p. 20 of Tame the BeaST or Q5 of the BibTeX FAQ. This has been the case for BibTeX since the start and carried over to Biber.

You can sort of get around this by using braces instead of quotes.

author    = {John S\"{o}ren},

works. This is one of the reasons why I prefer braces over quotes as field delimiters.

But really you should switch to {\"o} or even better ö. Even with old files it should not be too hard to do a search-and-replace on the problematic character macros.