# tcolorbox overlay app does not work

I'm trying to build this mwe taken from the tcolorbox manual p. 270 (I have simplified it a bit):

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{skins}

\tcbset{frogbox/.style={enhanced,colback=green!10,colframe=green!65!black,
enlarge top by=5.5mm,overlay={\foreach \x in {2cm,3.5cm} {
\begin{scope}[shift={([xshift=\x]frame.north west)}]
\path[draw=green!65!black,fill=green!10,line width=1mm] (0,0) arc (0:180:5mm);
\path[fill=black] (-0.2,0) arc (0:180:1mm);
\end{scope}}}]}}

\tcbset{app/.style={overlay app={%
\draw(frame.north)--(frame.south)}}}

\begin{document}
\begin{tcolorbox}[frogbox,title=My title]
This is a \textbf{tcolorbox}.
\end{tcolorbox}

\begin{tcolorbox}[frogbox,app,title=My title]
This is a \textbf{tcolorbox}.\par
Here, we apply a second overlay.
\end{tcolorbox}
\end{document}


The build fails with the following error:

! Package pgfkeys Error: I do not know the key '/tcb/overlay app', to which you passed '\draw (frame.north)--(frame.south)', and I am going to ignore it. Perhaps you misspelled it.

I'm using TL14 pretest, everything up-to-date. Is this a bug somewhere?

In order to be able to use the ... app or ... pre families of keys, you need to load the hooks library:

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{skins,hooks}

\tcbset{
frogbox/.style={
enhanced,
colback=green!10,
colframe=green!65!black,
enlarge top by=5.5mm,
overlay={
\foreach \x in {2cm,3.5cm} {
\begin{scope}[shift={([xshift=\x]frame.north west)}]
\path[draw=green!65!black,fill=green!10,line width=1mm] (0,0) arc (0:180:5mm);
\path[fill=black] (-0.2,0) arc (0:180:1mm);
\end{scope}
}
}
}
}

\tcbset{
app/.style={
overlay app={%
\draw(frame.north)--(frame.south);
}
}
}

\begin{document}
\begin{tcolorbox}[frogbox,title=My title]
This is a \textbf{tcolorbox}.
\end{tcolorbox}

\begin{tcolorbox}[frogbox,app,title=My title]
This is a \textbf{tcolorbox}.\par
Here, we apply a second overlay.
\end{tcolorbox}
\end{document}