Clarify elsewhen initial

Closes #2636

chapters/equations.tex

@@ -748,7 +748,7 @@ \section{Initialization, initial equation, and initial algorithm}\label{initiali
 (such as simulation or linearization).
 
 The equations of a when-clause are active during initialization, if and only if they are explicitly enabled with \lstinline!initial()!, and only in one of the two forms
-\lstinline!when initial() then! or \lstinline!when {$\ldots$, initial(), $\ldots$} then! (and similarly for algorithms see below).  In this case, the when-clause equations remain active during the
+\lstinline!when initial() then! or \lstinline!when {$\ldots$, initial(), $\ldots$} then! (and similarly for \lstinline!elsewhen!  and algorithms see below).  In this case, the when-clause equations remain active during the
 whole initialization phase.  In case of a \lstinline!reinit(x, expr)! being active during initialization (due to being inside \lstinline!when initial()!) this is interpreted as adding
 \lstinline!x = expr! (the \lstinline!reinit!-equation) as an initial equation.
 
@@ -762,6 +762,15 @@ \section{Initialization, initial equation, and initial algorithm}\label{initiali
 \lstinline!when initial() then! or \lstinline!when {$\ldots$, initial(), $\ldots$} then!. In this case, the algorithmic statements within the when-statement remain active during the whole
 initialization phase.
 
+An active when-clause inactivates the following \lstinline!elsewhen! (similarly as for when-clauses during simulation), but apart from that
+the first \lstinline!elsewhen initial() then! or \lstinline!elsewhen {$\ldots$, initial(), $\ldots$} then! is similarly active during initialization as
+\lstinline!when initial() then! or \lstinline!when {$\ldots$, initial(), $\ldots$} then!.
+
+\begin{nonnormative}
+That means that any subsequent \lstinline!elsewhen initial()! has no effect,
+similarly as \lstinline!when false then!.
+\end{nonnormative}
+
 \begin{nonnormative}
 There is no special handling of inactive when-statements during initialization, instead
 variables assigned in when-statements are initialized using \lstinline!v := pre(v)!