Explain use of quotes around code fragments

Fixes modelica#3191.

chapters/introduction.tex

@@ -130,6 +130,9 @@ \section{Notation}\label{notation}
 It is common to mix Modelica code with mathematical notation.
 For example, \lstinline!average($x$, $y$)! could be defined as $\frac{x + y}{2}$.
 
+Inline code fragments are sometimes surrounded by quotes to clearly mark their beginning and end, or to emphasize separation from the surrounding text.
+For example, `\lstinline!,!' is used to separate the arguments of a function call.
+
 \begin{definition}[Something]% Do not add this one to the index!
 Text defining the meaning of \emph{something}.
 \end{definition}

styleguide.md

@@ -189,6 +189,22 @@ Fixed ordinals: 1st, 2nd, 3rd.
 Symbolic ordinals: $n$th, $(n+1)$th.
 ```
 
+## Inline code
+
+Inline code is typically formatted using just the `\lstinline` macro.
+
+Since the change of type face can be very hard to notice for small code fragments, quotes may sometimes be used to emphasize the distinction from the surrounding text, unless the code fragment consists of a single identifier (consistent presentation of identifiers is given higher priority than clarity of presentation in this case).
+Use single quotes for a single letter code fragment, for example:
+```
+When automatically deriving a name, any trailing `\lstinline!1!' in the …
+```
+Use double quotes for a multi-letter code fragment, for example:
+```
+… and prepending the reduction expression with ``\lstinline!functionName(!''.
+```
+
+Avoid overusing quotes around code fragments, especially for multi-letter fragments.
+
 ## Code listings
 
 ### Modelica listings