<p>These <em>severities</em> are mapped into a smaller set (the
Diagnostic::Level enum, {<tt>Ignored</tt>, <tt>Note</tt>, <tt>Warning</tt>,
-<tt>Error</tt> }) of output <em>levels</em> by the diagnostics subsystem based
+<tt>Error</tt>, <tt>Fatal</tt> }) of output <em>levels</em> by the diagnostics
+subsystem based
on various configuration options. For example, if the user specifies
<tt>-pedantic</tt>, <tt>EXTENSION</tt> maps to <tt>Warning</tt>, if they specify
<tt>-pedantic-errors</tt>, it turns into <tt>Error</tt>. Clang also internally
supports a fully fine grained mapping mechanism that allows you to map any
diagnostic that doesn't have <tt>ERRROR</tt> severity to any output level that
you want. This is used to implement options like <tt>-Wunused_macros</tt>,
-<tt>-Wundef</tt> etc.</p>
+<tt>-Wundef</tt> etc. Fatal errors are considered so severe that diagnostics
+that occur after them are supressed as "almost certainly useless".</p>
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<h4>The Format String</h4>