In an RTL Wikipedia a heading like "==<span dir="ltr">C++</span>==" shows correctly as a heading in the text flow, but it is shown as "++C" in the table of contents, because the <span> tag is omitted and an RTL direction is assumed.
Not all HTML is omitted - a heading like "==E = mc<sup>2</sup>==" shows correctly both in the heading and in the table of contents.
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Severity: normal