example a class with a <code class="classname">std::string</code> member variable
  will have the same mangled name whether compiled with the old or new ABI.
  In order to detect such problems the new types and functions are
  annotated with the <span class="property">abi_tag</span> attribute, allowing the
  compiler to warn about potential ABI incompatibilities in code using them.
  Those warnings can be enabled with the <code class="option">-Wabi-tag</code> option.
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