QTextCharFormat tool tips not shown when using QSyntaxHighlighter

//! [0]
Highlighter::Highlighter(QTextDocument *parent)
    : QSyntaxHighlighter(parent)
{
    HighlightingRule rule;

    keywordFormat.setForeground(Qt::darkBlue);
    keywordFormat.setFontWeight(QFont::Bold);

    // THIS NEXT LINE SEEMS TO HAVE NO EFFECT
    keywordFormat.setToolTip("Test tooltip");

    QStringList keywordPatterns;
    keywordPatterns << "\\bchar\\b" << "\\bclass\\b" << "\\bconst\\b"
                    << "\\bdouble\\b" << "\\benum\\b" << "\\bexplicit\\b"
                    << "\\bfriend\\b" << "\\binline\\b" << "\\bint\\b"
                    << "\\blong\\b" << "\\bnamespace\\b" << "\\boperator\\b"
                    << "\\bprivate\\b" << "\\bprotected\\b" << "\\bpublic\\b"
                    << "\\bshort\\b" << "\\bsignals\\b" << "\\bsigned\\b"
                    << "\\bslots\\b" << "\\bstatic\\b" << "\\bstruct\\b"
                    << "\\btemplate\\b" << "\\btypedef\\b" << "\\btypename\\b"
                    << "\\bunion\\b" << "\\bunsigned\\b" << "\\bvirtual\\b"
                    << "\\bvoid\\b" << "\\bvolatile\\b";
    foreach (const QString &pattern, keywordPatterns) {
        rule.pattern = QRegExp(pattern);
        rule.format = keywordFormat;
        highlightingRules.append(rule);
//! [0] //! [1]
    }
//! [1]

//! [2]
    classFormat.setFontWeight(QFont::Bold);
    classFormat.setForeground(Qt::darkMagenta);
    rule.pattern = QRegExp("\\bQ[A-Za-z]+\\b");
    rule.format = classFormat;
    highlightingRules.append(rule);
//! [2]

//! [3]
    singleLineCommentFormat.setForeground(Qt::red);
    rule.pattern = QRegExp("//[^\n]*");
    rule.format = singleLineCommentFormat;
    highlightingRules.append(rule);

    multiLineCommentFormat.setForeground(Qt::red);
//! [3]

//! [4]
    quotationFormat.setForeground(Qt::darkGreen);
    rule.pattern = QRegExp("\".*\"");
    rule.format = quotationFormat;
    highlightingRules.append(rule);
//! [4]

//! [5]
    functionFormat.setFontItalic(true);
    functionFormat.setForeground(Qt::blue);
    rule.pattern = QRegExp("\\b[A-Za-z0-9_]+(?=\\()");
    rule.format = functionFormat;
    highlightingRules.append(rule);
//! [5]

//! [6]
    commentStartExpression = QRegExp("/\\*");
    commentEndExpression = QRegExp("\\*/");
}