[intro.defs] Define "warning"

Author: Eisenwave

source/intro.tex

@@ -694,6 +694,18 @@
 \tcode{false}.
 \end{example}
 
+\indexdefn{warning}%
+\definition{warning}{defns.warning}
+message belonging to a subset of
+\termref{defns.diagnostic}{diagnostic message}{s}
+produced to provide the user with information about the program,
+not as a consequence of a \Cpp{} program being rejected
+
+\begin{example}
+The \tcode{#warning} directive produces a warning.
+The \tcode{#error} directive produces a diagnostic message that is not a warning\iref{cpp.error}.
+\end{example}
+
 \indexdefn{program!well-formed}%
 \definition{well-formed program}{defns.well.formed}
 \Cpp{} program constructed according to the syntax and semantic rules