More advanced elaboration. (modelica#3241)

* More advanced elaboration.
Specifically this allows hieararchical additions in buses
 - if the penultimate component is potentially present.
Closes modelica#3147
* Apply suggestions from code review

Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>
Co-authored-by: Elena Shmoylova <eshmoylova@users.noreply.github.com>

chapters/connectors.tex

@@ -107,9 +107,14 @@ \subsection{Expandable Connectors}\label{expandable-connectors}
 This applies to both variables of simple types, and variables of structured types.
 
 Then connections containing expandable connectors are elaborated:
-\begin{itemize}
+\begin{enumerate}
+\item
+  If a connect-equation references a potentially present component \emph{as part of the argument} it will be marked as being present, which will allow a connection to an undeclared connector inside it.
+  The rule does not apply for the complete argument.
 \item
-  One connector in the \lstinline!connect!-equation must reference a declared component, and if the other connector is an undeclared element in a declared expandable connector it is handled as follows (elements that are only potentially present are not seen as declared):
+  After that at least one connector in the connect equation must reference a declared component.
+\item
+  If the other connector is undeclared it must be in a declared component and is handled as follows:
   \begin{itemize}
   \item
     The expandable connector instance is automatically augmented with a new component having the used name and corresponding type.
@@ -124,7 +129,10 @@ \subsection{Expandable Connectors}\label{expandable-connectors}
     \end{nonnormative}
     For an array the \lstinline!input!/\lstinline!output! property can be deduced separately for each array element.
   \end{itemize}
+\end{enumerate}
 
+Additionally:
+\begin{itemize}
 \item
   When two expandable connectors are connected, each is augmented with the variables that are only declared in the other expandable connector (the new variables are neither \lstinline!input! nor \lstinline!output!).
   This is repeated until all connected expandable connector instances have matching variables.