//! [0] in Qt source code

Question

What is the meaning of the //! [n] (n = 0, 1, 2 ...) markup in the C++/QML sources in the Qt sample projects?

For example:

//! [0]
GLWidget::GLWidget(Helper *helper, QWidget *parent)
    : QGLWidget(QGLFormat(QGL::SampleBuffers), parent), helper(helper)
{
    elapsed = 0;
    setFixedSize(840, 400);
    setAutoFillBackground(false);
}
//! [0]

//! [1]
void GLWidget::animate()
{
    elapsed = (elapsed + qobject_cast<QTimer*>(sender())->interval()) % 1000;
    repaint();
}
//! [1]

//! [2]
void GLWidget::paintEvent(QPaintEvent *event)
{
    QPainter painter;
    painter.begin(this);
    painter.setRenderHint(QPainter::Antialiasing);
    helper->paint(&painter, event, elapsed);
    painter.end();
}
//! [2]

Answer 1

Despite the common misconception, this is qdoc syntax, not doxygen. This comment is for documentation purposes in the Qt Project to mark example snippets to be rendered so. It is not really documented well, but here you can find the corresponding code that implements this feature.

As an end user of Qt, you do not need to deal with it too much unless you start contributing to the Qt Project itself or you are trying to reuse qdoc for your own project, which would be admittedly odd at this point.