Why does biblatex not process global options

Question

For some reason biblatex doesn't seem to be reading global options. The following tex file produces a single citation, but not in the authoryear style. If I uncomment the PassOptionsToPackage line, it works appropriately, but I'd like to pass the options directly in the class definition. Is there a reason for why the style option isn't getting read by biblatex? biblatex does seem to be processing the backend=biber option, because it doesn't produce a warning indicating that no backend was specified, which it does when that option is removed.

\RequirePackage{filecontents}

\begin{filecontents}{myclass.cls}
\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{myclass}[2016/10/18 1.0 current]
\LoadClass{article}
\RequirePackage{biblatex}
\end{filecontents}

\begin{filecontents}{references.bib}
@article{hello,
    title={Hello World},
    author={Bar, Foo},
    journal={Baz},
    year=2016,
}                
\end{filecontents}

%\PassOptionsToPackage{style=authoryear}{biblatex}
\documentclass[backend=biber,style=authoryear]{myclass}
\bibliography{references}
\begin{document}
\textcite{hello}
\printbibliography
\end{document}

Answer 1

Global options are stored in \@classoptionslist. The \ProcessOptions command in a package checks this lists and compares every entry with the list of declared options of the package. If the option is known, it is executed.

But style=authoryear is not a declared, known option of biblatex. The package doesn't contain a long list of \DeclareOption{style=authoryear}{...}, \DeclareOption{style=authortitle}{...} settings. This would be neither practical nor flexible enough: after all external packages can define their own styles.

So biblatex uses a clever trick: It changes with \DeclareOption* the handling of unknown options. By default LaTeX issues \@unknownoptionerror for unknown options, but biblatex passes all options to the keyval handler.

This means that by default global options are ignored. You could pass them to biblatex, but if the option list contains options not known by biblatex you would get errors. So you will have either to "declare" all the potential options for biblatex, or change the key handler of biblatex. E.g. like this

\documentclass[style=authoryear,german]{book}

\usepackage{kvoptions}
\makeatletter

\let\setkeys\kvsetkeys
\kv@set@family@handler {blx@opt@pre} {\PackageWarning{biblatex}{Unused option #1}}

\PassOptionsToPackage{\@classoptionslist}{biblatex}
\usepackage{biblatex}

\addbibresource{biblatex-examples.bib}
\begin{document}
\cite{doody}

\end{document}