alt in sequence diagram with pgf-umlsd

I am doing a sequence diagram but the sdblock enviroment doesn't allow me to do an alt block with two alternatives, I have this:

\documentclass{standalone}
\usepackage{pgf-umlsd}
\begin{document}
\begin{sequencediagram}
\newinst{u}{User}
\newinst[4]{s}{System}
\mess{u}{aCall}{s}
\begin{sdblock}{alt}{[x=3]}
\mess{u}{otherCall}{s}
\end{sdblock}
\end{sequencediagram}
\end{document}


But it only has one part in the alt, I want to make the "else", also I know that I can achieve it with tizk-uml, but with this during a call, the dotted line below a instance is a rectangle and I don't want the rectangle.

How can I do the "else" in alt with pgf-umlsd or avoid the rectangle in tikz-uml?

• Could you show us the corresponding code for tikz-uml? – Torbjørn T. Aug 31 '17 at 20:06