+<p>N.B. although there are precondition checks for some string operations,
+e.g. <code>operator[]</code>,
+they will not always be run when using the <code>char</code> and
+<code>wchar_t</code> specialisations (<code>std::string</code> and
+<code>std::wstring</code>). This is because libstdc++ uses GCC's
+<code>extern template</code> extension to provide explicit instantiations
+of <code>std::string</code> and <code>std::wstring</code>, and those
+explicit instantiations don't include the debug-mode checks. If the
+containing functions are inlined then the checks will run, so compiling
+with <code>-O1</code> might be enough to enable them. Alternatively
+<code>-D_GLIBCXX_EXTERN_TEMPLATE=0</code> will suppress the declarations
+of the explicit instantiations and cause the functions to be instantiated
+with the debug-mode checks included, but this is unsupported and not
+guaranteed to work. For full debug-mode support you can use the
+<code>__gnu_debug::basic_string</code> debugging container directly,
+which always works correctly.
+</p>